Tag Archives: Solar and Stellar Astrophysics

Updating the $^{56}$Ni Problem in Core-collapse Supernova Explosion [HEAP]

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http://arxiv.org/abs/2301.03610


Details of the core-collapse supernova (CCSN) explosion mechanism still need to be fully understood. There is an increasing number of successful examples of reproducing explosions in multidimensional hydrodynamic simulations, but subsequent studies pointed out that the growth rates of the explosion energy $\dot{E}\mathrm{expl}$ of these simulations are insufficient to produce enough $^{56}$Ni to match observations. This issue is known as the `$^{56}$Ni problem’ in CCSNe. Recently, however, some studies have suggested that this $^{56}$Ni problem is derived from the simplicity of the explosion model. In response, we investigate the effect of the explosion energy growth rate $\dot{E}\mathrm{expl}$ on the behavior of nucleosynthesis in CCSNe in a more realistic model. We employ the 1D Lagrangian hydrodynamic code, in which we take neutrino heating and cooling terms into account with the light-bulb approximation. We reiterate that, consistent with previous rebuttal studies, there is the $^{56}$Ni problem: Although $^{56}$Ni is synthesized to almost the same mass coordinate independent of $\dot{E}\mathrm{expl}$, some of the innermost material in the low-$\dot{E}\mathrm{expl}$ model failed to escape, leading to a shift in the innermost mass coordinate of the ejecta to the outer positions. Comparing our results with observations, we find that while modern slow explosions can, in principle, reproduce observations of standard Type II SNe, this is not possible with stripped-envelope SNe. Our finding places a strong constraint on the explosion mechanism. There are significant differences in the progenitor structures and the explosion mechanism between Type II and stripped-envelope SNe.

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R. Sawada and Y. Suwa
Wed, 11 Jan 23
51/80

Comments: 14 pages, 11 figures, submitted to ApJ

Detecting isolated stellar-mass black holes by the Roman telescope [GA]

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http://arxiv.org/abs/2301.03812


Isolated Stellar-Mass BlackHoles (ISMBHs) are potentially discernible through microlensing observations. In this work, we study detecting and characterizing ISMBHs with the Roman observations. We simulate a big ensemble of these events as seen by Roman and estimate the errors in the physical parameters of the lens objects, including their masses, distances, and proper motions through calculating Fisher and Covariance matrices. Since the ~2.3-year time gap between Roman’s first three observing seasons and the others may lower the efficiency of realizing microlensing events and characterizing ISMBHs, we additionally consider a scenario where we add a small amount of additional observations — one hour of observations every 10 days when the Bulge is observable during the large time gap — which is equivalent to a total of about one additional day of observations with the Roman telescope. These extra observations increase Roman’s efficiency for characterizing ISMBHs by ~$1-2\%$ and, more importantly, improve the robustness of the results by avoiding possible degenerate solutions. By considering uniform, and power-law mass functions ($dN/dM ~ M^{-\alpha}$, $\alpha=2,~1,~0.5$) for ISMBHs in the range of $[2,~50] M_{\odot}$, we conclude that the Roman telescope will determine the physical parameters of the lenses within $<5\%$ uncertainty, with efficiencies of $21\%$, and $16$-$18\%$, respectively. By considering these mass functions, we expect that the Roman telescope during its mission will detect and characterize $3$-$4$, $15$-$17$ and $22$-$24$ ISMBHs through astrometric microlensing, with the relative errors for all physical parameters less than $1,~5,~10\%$, respectively. Microlensing events owing to ISMBHs with a mass $\simeq 10$-$25 M_{\odot}$ and located close to the observer with $D_l \lesssim 0.5 D_s$ while the source is inside the Galactic disk can be characterized with least errors.

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S. Sajadian and K. Sahu
Wed, 11 Jan 23
56/80

Comments: 15 pages, 6 figures (23 panels), accepted for publication in AJ

The carbon star mystery: forty years later [SSA]

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http://arxiv.org/abs/2301.03978


In 1981 Icko Iben Jr published a paper entitled ‘The carbon star mystery: why do the low mass ones become such, and where have all the high mass ones gone?’, where he discussed the discrepancy between the theoretical expectation and its observational counterpart about the luminosity function of AGB carbon stars. After more than 40 years, our understanding of this longstanding problem is greatly improved, also thanks to more refined stellar models and a growing amount of observational constraints. In this paper we review the state of the art of these studies and we briefly illustrate the future perspectives.

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O. Straniero, C. Abia and I. Dominguez
Wed, 11 Jan 23
60/80

Comments: Review paper to be published in EPJA Special Issue on: ‘From reactors to stars’

A Spectroscopic Analysis of a Sample of K2 Planet-Host Stars: Stellar Parameters, Metallicities and Planetary Radii [SSA]

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http://arxiv.org/abs/2301.03961


The physical properties of transiting exoplanets are connected with the physical properties of their host stars. We present a homogeneous spectroscopic analysis based on spectra of FGK-type stars observed with the Hydra spectrograph on the WIYN telescope. We derived effective temperatures, surface gravities, and metallicities, for 81 stars observed by K2 and 33 from Kepler 1. We constructed an Fe I and II line list that is adequate for the analysis of R$\sim$18,000 spectra covering 6050-6350 \r{A} and adopted the spectroscopic technique based on equivalent width measurements. The calculations were done in LTE using Kurucz model atmospheres and the qoyllur-quipu (q$^2$) package. We validated our methodology via analysis of a benchmark solar twin and solar proxies, which are used as the solar reference. We estimated the effects that including Zeeman sensitive Fe I lines have on the derived stellar parameters for young and possibly active stars in our sample and found it not to be significant. Stellar masses and radii were derived by combining the stellar parameters with Gaia EDR3 and V magnitudes and isochrones. The measured stellar radii have 4.2\% median internal precision, leading to a median internal uncertainty of 4.4\% in the derived planetary radii. With our sample of 83 confirmed planets orbiting K2 host stars, the radius gap near R${planet}1.9R{\plus}$ is detected, in agreement with previous findings. Relations between the planetary radius, orbital period and metallicity are explored and these also confirm previous findings for Kepler 1 systems.

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V. Loaiza-Tacuri, K. Cunha, V. Smith, et. al.
Wed, 11 Jan 23
67/80

Comments: 35 pages, 17 figures

LS And: WZ Sge-type outburst first time since the 1971 discovery [SSA]

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http://arxiv.org/abs/2301.03743


LS And was a transient discovered in 1971 in the M31 region and it has been argued whether it could be an intergalactic nova or a dwarf nova. Using the Zwicky Transient Facility (ZTF) data, I found that the object underwent the second known outburst in 2022 April. The behavior was that of a WZ Sge-type dwarf nova with a long fading tail and the light curves of the 1971 and 2022 outbursts matched very well. The light curves suggest that LS And is a typical WZ Sge-type dwarf nova near (but before reaching) the period minimum of cataclysmic variables. The true observed peak of the 1971 outburst was likely 12.2 mag. The outburst parameters were similar to those of other WZ Sge-type dwarf novae. The fading tail lasts more than a year and the object is still currently on this tail. There was a hint of 0.5-mag temporary brightening on the fading tail and the object appears still active after the outburst.

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T. Kato
Wed, 11 Jan 23
69/80

Comments: 9 pages, 4 figures, VSOLJ Variable Star Bulletin No. 105

TESS-Gaia Light Curve: a PSF-based TESS FFI light curve product [IMA]

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http://arxiv.org/abs/2301.03704


The Transiting Exoplanet Survey Satellite (TESS) is continuing its second extended mission after 55 sectors of observations. TESS publishes full-frame images (FFI) at a cadence of 1800, 600, or 200 seconds, allowing light curves to be extracted for stars beyond a limited number of pre-selected stars. Simulations show that thousands of exoplanets, eclipsing binaries, variable stars, and other astrophysical transients can be found in these FFI light curves. To obtain high-precision light curves, we forward model the FFI with the effective point spread function to remove contamination from nearby stars. We adopt star positions and magnitudes from Gaia DR3 as priors. The resulting light curves, called TESS-Gaia Light Curves (TGLC), show a photometric precision closely tracking the pre-launch prediction of the noise level. TGLC’s photometric precision reaches <~2% at 16th TESS magnitude even in crowded fields. We publish TGLC Aperture and PSF light curves for stars down to 16th TESS magnitude through the Mikulski Archive for Space Telescopes (MAST) for all available sectors and will continue to deliver future light curves via DOI: 10.17909/610m-9474. The open-source package tglc is publicly available to enable any user to produce customized light curves.

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T. Han and T. Brandt
Wed, 11 Jan 23
76/80

Comments: 23 pages, 13 figures, 4 tables, AJ accepted. Light curves are available at this https URL tglc package is pip-installable and available at this https URL

Multiple injections of energetic electrons associated with the flare/CME event on 9 October 2021 [SSA]

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http://arxiv.org/abs/2301.03650


We study the solar energetic particle (SEP) event observed on 9 October 2021, by multiple spacecraft including Solar Orbiter (SolO). The event was associated with an M1.6 flare, a coronal mass ejection (CME) and a shock wave. During the event, high-energy protons and electrons were recorded by multiple instruments located within a narrow longitudinal cone. An interesting aspect of the event was the multi-stage particle energization during the flare impulsive phase and also what appears to be a separate phase of electron acceleration detected at SolO after the flare maximum. We aim to investigate and identify the multiple sources of energetic electron acceleration. We utilize SEP electron observations from the Energetic Particle Detector (EPD) and hard X-ray (HXR) observations from the Spectrometer/Telescope for Imaging X-rays (STIX) on-board SolO, in combination with radio observations at a broad frequency range. We focus on establishing an association between the energetic electrons and the different HXR and radio emissions associated with the multiple acceleration episodes. We have found that the flare was able to accelerate electrons for at least 20 minutes during the nonthermal phase observed in the form of five discrete HXR pulses. We also show evidence that the shock wave has contributed to the electron acceleration during and after the impulsive flare phase. The detailed analysis of EPD electron data shows that there was a time difference in the release of low- and high-energy electrons, with the high-energy release delayed. Also, the observed electron anisotropy characteristics suggest different connectivity during the two phases of acceleration.

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I. Jebaraj, A. Koulooumvakos, N. Dresing, et. al.
Wed, 11 Jan 23
77/80

Comments: 17 pages, 10 figures (main text). 3 pages, 3 figures (appendix). In review

Molecular Mapping of DR Tau's Protoplanetary Disk, Envelope, Outflow, and Large-Scale Spiral Arm [SSA]

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http://arxiv.org/abs/2301.02674


DR Tau has been noted for its unusually high variability in comparison with other T Tauri stars. Although it is one of the most extensively studied pre-main sequence stars, observations with millimeter interferometry have so far been relatively limited. We present NOEMA images of $^{12}$CO, $^{13}$CO, C$^{18}$O, SO, DCO$^+$, and H$_2$CO toward DR Tau at a resolution of $\sim0.5”$ ($\sim100$ au). In addition to the protoplanetary disk, CO emission reveals an envelope, a faint asymmetric outflow, and a spiral arm with a clump. The $\sim1200$ au extent of the CO arm far exceeds that of the spiral arms previously detected in scattered light, which underlines the necessity of sensitive molecular imaging for contextualizing the disk environment. The kinematics and compact emission distribution of C$^{18}$O, SO, DCO$^+$, and H$_2$CO indicate that they originate primarily from within the Keplerian circumstellar disk. The SO emission, though, also exhibits an asymmetry that may be due to interaction with infalling material or unresolved substructure. The complex environment of DR Tau is reminiscent of those of outbursting FUor sources and some EXor sources, suggesting that DR Tau’s extreme stellar activity could likewise be linked to disk instabilities promoted by large-scale infall.

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J. Huang, E. Bergin, J. Bae, et. al.
Tue, 10 Jan 23
11/93

Comments: 29 pages, accepted by ApJ

Bridging High-Density, Electron Beam Coronal Transport and Deep Chromospheric Heating in Stellar Flares [SSA]

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http://arxiv.org/abs/2301.03477


The optical and near-ultraviolet (NUV) continuum radiation in M dwarf flares is thought to be the impulsive response of the lower stellar atmosphere to magnetic energy release and electron acceleration at coronal altitudes. This radiation is sometimes interpreted as evidence of a thermal photospheric spectrum with $T \approx 10^4$ K. However, calculations show that standard solar flare coronal electron beams lose their energy in a thick target of gas in the upper and middle chromosphere (log${10}$ column mass /[g cm$^{-2}$] $\lesssim -3$). At larger beam injection fluxes, electric fields and instabilities are expected to further inhibit propagation to low altitudes. We show that recent numerical solutions of the time-dependent equations governing the power-law electrons and background coronal plasma (Langmuir and ion-acoustic) waves from Kontar et al. produce order-of-magnitude larger heating rates than occur in the deep chromosphere through standard solar flare electron beam power-law distributions. We demonstrate that the redistribution of beam energy above $E \gtrsim 100$ keV in this theory results in a local heating maximum that is similar to a radiative-hydrodynamic model with a large, low-energy cutoff and a hard power-law index. We use this semi-empirical forward modeling approach to produce opaque NUV and optical continua at gas temperatures $T \gtrsim 12,000$ K over the deep chromosphere with log${10}$ column mass /[g cm$^{-2}$] of $-1.2$ to $-2.3$. These models explain the color temperatures and Balmer jump strengths in high-cadence M dwarf flare observations, and they clarify the relation among atmospheric, radiation, and optical color temperatures in stellar flares.

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A. Kowalski
Tue, 10 Jan 23
13/93

Comments: 12 pages, 4 figures, accepted for publication in the Astrophysical Journal Letters

Impact of opacity effects on chromospheric oscillations inferred from NLTE inversions [SSA]

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http://arxiv.org/abs/2301.03273


Chromospheric inferences rely on the interpretation of spectral lines that are formed under Non-Local Thermodynamic Equilibrium (NLTE) conditions. In the presence of oscillations, changes in the opacity impact the response height of the spectral lines and hinder the determination of the real properties of the fluctuations. We aim to explore the relationship between the chromospheric oscillations inferred by NLTE inversion codes and the waves’ intrinsic fluctuations in velocity and temperature. Numerical simulations of wave propagation in an umbra have been computed with the code MANCHA. The NLTE synthesis and inversion code NICOLE has been used to compute spectropolarimetric Ca II 8542 \AA\ line profiles for the models obtained from the simulations. The synthetic profiles have been inverted and the inferences from the inversions have been compared with the known simulated atmospheres. NLTE inversions of the Ca II 8542 \AA\ line capture low-frequency oscillations, including those in the main band of chromospheric oscillations around 6 mHz. In contrast, waves with frequencies above 9 mHz are poorly characterized. Velocity oscillations at those higher frequencies exhibit clear indications of opacity fluctuations. The main response of the line to velocity fluctuations comes from low chromospheric heights, whereas the response to temperature shows sudden jumps between the high photosphere and the low chromosphere. This strong variation in the heights where the line is sensitive to temperature is revealed as a strong oscillatory power in the inferred fluctuations. Our results validate the use of NLTE inversions to study chromospheric oscillations with frequencies below 9 mHz. The interpretation of higher frequency oscillations and the power of temperature oscillations must be addressed with care since they exhibit signatures of opacity oscillations.

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T. Felipe and H. Socas-Navarro
Tue, 10 Jan 23
18/93

Comments: Abstract abridged for arXiv submission

Evidence of high-mass star formation through multi-scale mass accretion in hub-filament-system clouds [GA]

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http://arxiv.org/abs/2301.03144


We present a statistical study of a sample of 17 hub-filament-system (HFS) clouds of high-mass star formation using high-angular resolution ($\sim$1-2 arcsecond) ALMA 1.3mm and 3mm continuum data. The sample includes 8 infrared (IR)-dark and 9 IR-bright types, which correspond to an evolutionary sequence from the IR-dark to IR-bright stage. The central massive clumps and their associated most massive cores are observed to follow a trend of increasing mass ($M$) and mass surface density ($\Sigma$) with evolution from IR-dark to IR-bright stage. In addition, a mass-segregated cluster of young stellar objects (YSOs) are revealed in both IR-dark and IR-bright HFSs with massive YSOs located in the hub and the population of low-mass YSOs distributed over larger areas. Moreover, outflow feedback in all HFSs are found to escape preferentially through the inter-filamentary diffuse cavities, suggesting that outflows would render a limited effect on the disruption of the HFSs and ongoing high-mass star formation therein. From the above observations, we suggest that high-mass star formation in the HFSs can be described by a multi-scale mass accretion/transfer scenario, from hub-composing filaments through clumps down to cores, that can naturally lead to a mass-segregated cluster of stars.

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H. Liu, A. Tej, T. Liu, et. al.
Tue, 10 Jan 23
20/93

Comments: Accepted for publication in MNRAS; 16 pages, 8 figures, and 3 tables

Reflections on nebulae around young stars: A systematic search for late-stage infall of material onto Class II disks [SSA]

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http://arxiv.org/abs/2301.02994


Context. While it is generally assumed that Class II sources evolve largely in isolation from their environment, many still lie close to molecular clouds and may continue to interact with them. This may result in late accretion of material onto the disk that can significantly influence disk processes and planet formation.
Aims. In order to systematically study late infall of gas onto disks, we identify candidate Class II sources in close vicinity to a reflection nebula (RN) that may be undergoing this process.
Methods. First we targeted Class II sources with known kilo-au scale gas structures – possibly due to late infall of material – and we searched for RNe in their vicinity in optical and near-infrared images. Second, we compiled a catalogue of Class II sources associated with RNe and looked for the large-scale CO structures in archival ALMA data. Using the catalogues of protostars and RNe, we also estimated the probability of Class II sources interacting with surrounding material.
Results. All of the sources with large-scale gas structures also exhibit some reflection nebulosity in their vicinity. Similarly, at least five Class II objects associated with a prominent RNe, and for which adequate ALMA observations are available, were found to have spirals or stream-like structures which may be due to late infall. We report the first detection of these structures around S CrA.
Conclusions. Our results suggest that a non-negligible fraction of Class II disks in nearby star-forming regions may be associated with RNe and could therefore be undergoing late accretion of gas. Surveys of RNe and kilo-au scale gas structures around Class II sources will allow us to better understand the frequency and impact of late-infall phenomena.

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A. Gupta, A. Miotello, C. Manara, et. al.
Tue, 10 Jan 23
21/93

Comments: Accepted for publication in Astronomy & Astrophysics

Highly Energetic Electrons Accelerated in Strong Solar Flares as a Preferred Driver of Sunquakes [SSA]

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http://arxiv.org/abs/2301.02865


Sunquakes are enhanced seismic waves excited in some energetic solar flares. Up to now, their origin has still been controversial. In this Letter, we select and study 20 strong flares in Solar Cycle 24, whose impulse phase is fully captured by the \emph{Reuven Ramaty High Energy Solar Spectroscopic Imager} (\emph{RHESSI}). For 11 out of 12 sunquake-active flares in our sample, the hard X-ray (HXR) emission shows a good temporal and spatial correlation with the white-light (WL) enhancement and the sunquake. Spectral analysis also reveals a harder photon spectrum that extends to several hundred keV, implying a considerable population of flare-accelerated nonthermal electrons at high energies. Quantitatively, the total energy of electrons above 300 keV in sunquake-active flares is systematically different from that in sunquake-quiet flares, while the difference is marginal for electrons above 50 keV. All these facts support highly energetic electrons as a preferred driver of the sunquakes. Such an electron-driven scenario can be reasonably accommodated in the framework of a recently proposed selection rule for sunquake generation. For the remaining one event, the sunquake epicenter is cospatial with a magnetic imprint, i.e., a permanent change of magnetic field on the photosphere. Quantitative calculation shows that the flare-induced downward Lorentz force can do enough work to power the sunquake, acting as a viable sunquake driver for this specific event.

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H. Wu, Y. Dai and M. Ding
Tue, 10 Jan 23
26/93

Comments: 11 pages, including 1 table and 4 figures. Accepted for publication in ApJL

The evolution of phase space densities in star-forming regions [GA]

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http://arxiv.org/abs/2301.03472


The multi-dimensional phase space density (both position and velocity) of star-forming regions may encode information on the initial conditions of star and planet formation. Recently, a new metric based on the Mahalanobis distance has been used to show that hot Jupiters are more likely to be found around exoplanet host-stars in high 6D phase space density, suggesting a more dynamic formation environment for these planets. However, later work showed that this initial result may be due to a bias in the age of hot Jupiters and the kinematics of their host stars. We test the ability of the Mahalanobis distance and density to differentiate more generally between star-forming regions with different morphologies by applying it to static regions that are either substructured or smooth and centrally concentrated. We find that the Mahalanobis distance is unable to distinguish between different morphologies, and that the initial conditions of the N-body simulations cannot be constrained using only the Mahalanobis distance or density. Furthermore, we find that the more dimensions in the phase space the less effective the Mahalanobis density is at distinguishing between different initial conditions. We show that a combination of the mean three-dimensional (x, y, z) Mahalanobis density and the Q-parameter for a region can constrain its initial virial state. However this is due to the discriminatory power of the Q-parameter and not from any extra information imprinted in the Mahalanobis density. We therefore recommend continued use of multiple diagnostics for determining the initial conditions of star-forming regions, rather than relying on a single multi-dimensional metric.

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G. Blaylock-Squibbs and R. Parker
Tue, 10 Jan 23
28/93

Comments: 13 pages + appendices, 10 figures, accepted for publication in MNRAS

The messy death of a multiple star system and the resulting planetary nebula as observed by JWST [SSA]

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http://arxiv.org/abs/2301.02775


Planetary nebulae (PNe), the ejected envelopes of red giant stars, provide us with a history of the last, mass-losing phases of 90 percent of stars initially more massive than the Sun. Here, we analyse James Webb Space Telescope (JWST) Early Release Observation (ERO) images of the PN NGC3132. A structured, extended H2 halo surrounding an ionised central bubble is imprinted with spiral structures, likely shaped by a low-mass companion orbiting the central star at 40-60 AU. The images also reveal a mid-IR excess at the central star interpreted as a dusty disk, indicative of an interaction with another, closer companion. Including the previously known, A-type visual companion, the progenitor of the NGC3132 PN must have been at least a stellar quartet. The JWST images allow us to generate a model of the illumination, ionisation and hydrodynamics of the molecular halo, demonstrating the power of JWST to investigate complex stellar outflows. Further, new measurements of the A-type visual companion allow us to derive the value for the mass of the progenitor of a central star to date with excellent precision: 2.86+/-0.06 Mo. These results serve as path finders for future JWST observations of PNe providing unique insight into fundamental astrophysical processes including colliding winds, and binary star interactions, with implications for supernovae and gravitational wave systems.

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O. Marco, M. Akashi, S. Akras, et. al.
Tue, 10 Jan 23
35/93

Comments: 32 pages, 5 figures for the main article. 12 pages 8 figures for the supplementary material

The pristine nature of SMSS 1605$-$1443 revealed by ESPRESSO [SSA]

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http://arxiv.org/abs/2301.02678


SMSS J160540.18$-$144323.1 is the carbon-enhanced metal-poor (CEMP) star with the lowest iron abundance ever measured, [Fe/H]=-6.2, which was first reported with the SkyMapper telescope. The carbon abundance is A(C)~6.1 in the low-C band, as the majority of the stars in this metallicity range. Yet, constraining the isotopic ratio of key species, such as carbon, sheds light on the properties and origin of these elusive stars. We performed high-resolution observations of SMSS1605$-$1443 with the ESPRESSO spectrograph to look for variations in the radial velocity ($v_{rad}$) with time. These data have been combined with older MIKE and UVES archival observations to enlarge the temporal baseline. The $^{12}$C/$^{13}$C isotopic ratio is also studied to explore the possibility of mass transfer from a binary companion. A cross-correlation function against a natural template was applied to detect $v_{rad}$ variability and a spectral synthesis technique was used to derive $^{12}$C/$^{13}$C in the stellar atmosphere. We confirm previous indications of binarity in SMSS1605$-$1443 and measured a lower limit $^{12}$C/$^{13}$C$>60$ at more than a 3$\sigma$ confidence level, proving that this system is chemically unmixed and that no mass transfer from the unseen companion has happened so far. Thus, we confirm the CEMP-no nature of SMSS1605$-$1443 and show that the pristine chemical composition of the cloud from which it formed is currently imprinted in its stellar atmosphere free of contamination.

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D. Aguado, E. Caffau, P. Molaro, et. al.
Tue, 10 Jan 23
46/93

Comments: Published in A&A, 9 pages, 6 figures

Evolution of elemental abundances in hot active region cores from Chandrayaan-2 XSM observations [SSA]

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http://arxiv.org/abs/2301.03519


The First Ionization Potential (FIP) bias, whereby elemental abundances for low FIP elements in different coronal structures vary from their photospheric values and may also vary with time, has been widely studied. In order to study the temporal variation, and to understand the physical mechanisms giving rise to the FIP bias, we have investigated the hot cores of three ARs using disk-integrated soft X-ray spectroscopic observation with the Solar X-ray Monitor (XSM) onboard Chandrayaan-2. Observations for periods when only one AR was present on the solar disk were used so as to ensure that the AR was the principal contributor to the total X-ray intensity. The average values of temperature and EM were ~3 MK and 3.0E46/cm3 respectively. Regardless of the age and activity of the AR, the elemental abundances of the low FIP elements, Al, Mg, and Si were consistently higher than their photospheric values. The average FIP bias for Mg and Si was ~3, whereas the FIP bias for the mid-FIP element, S, was ~1.5. However, the FIP bias for the lowest FIP element, Al, was observed to be higher than 3, which, if real, suggests a dependence of the FIP bias of low FIP elements on their FIP value. Another major result from our analysis is that the FIP bias of these elements is established in within ~10 hours of emergence of the AR and then remains almost constant throughout its lifetime.

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B. Mondal, S. Vadawale, G. Zanna, et. al.
Tue, 10 Jan 23
52/93

Comments: Submitted to the Astrophysical Journal, 16 pages,8 figures

The Abundance of Belatedly Habitable Planets and Ambiguities in Definitions of the Continuously Habitable Zone [EPA]

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http://arxiv.org/abs/2301.02961


A planet’s history dictates its current potential to host habitable conditions and life. The concept of the Continuously Habitable Zone (CHZ) has been used to define the region around a star most likely to host planets with long-term habitability. However, definitions of the CHZ vary in the literature and often conflict with each other. Calculating the fraction of habitable zone planets in the CHZ as a function of stellar properties, we find that the quality of a star as a host for planets with long-term habitability and biosignatures depends strongly on the formulation of the CHZ used. For instance, older M stars are either excellent or sub-optimal hosts for CHZ planets, depending on whether one’s definition of habitability prioritizes the total time spent in the habitable zone or the continuity of habitable conditions from the delivery of volatiles to its current age. In this study, we focus on Belatedly Habitable Zone (BHZ) planets, i.e. planets which enter the habitable zone after formation due to the evolution of their host star. We find that between ~29-74% of planets in the habitable zone belong to this class of BHZ planets depending on the timescale for the delivery of volatiles. Whether these planets can retain their volatiles and support habitable conditions is unclear. Since BHZ planets comprise a large portion of the planets we expect to survey for biosignatures with future missions, the open question of their habitability is an important factor for mission design, survey strategies, and the interpretation of results.

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N. Tuchow and J. Wright
Tue, 10 Jan 23
53/93

Comments: Accepted for publication in The Astrophysical Journal

Twenty-five years of exoplanet discoveries: The exoplanet hosts [EPA]

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http://arxiv.org/abs/2301.03442


For centuries, humanity wondered if there were other worlds like ours in the Universe. For about a quarter of a century, we have known that planetary systems exist around other stars, and more than 3800 exoplanetary systems have been discovered so far. However, the large majority of the exoplanets remain invisible to us since we usually infer their presence by their effect on their star. The chapter is devoted to stellar hosts and their characteristics, emphasizing their description by discovery method and links between the properties of the host stars and their planets. The star-planet connection is vital to constrain the theories on the formation and evolution of planetary systems, including our own.

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B. Rojas-Ayala
Tue, 10 Jan 23
60/93

Comments: 21 pages, 10 figures; accepted as a chapter in the book “Planetary systems now”, eds. Luisa M. Lara and David Jewitt, World Scientific Publishing Co Pte Ltd

Cut-off of transverse waves through the solar transition region [SSA]

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http://arxiv.org/abs/2301.03100


Context. Transverse oscillations are ubiquitously observed in the solar corona, both in coronal loops and open magnetic flux tubes. Numerical simulations suggest that their dissipation could heat coronal loops, counterbalancing radiative losses. These models rely on a continuous driver at the footpoint of the loops. However, analytical works predict that transverse waves are subject to a cut-off in the transition region. It is thus unclear whether they can reach the corona, and indeed heat coronal loops. Aims. Our aims are to determine how the cut-off of kink waves affects their propagation into the corona, and to characterize the variation of the cut-off frequency with altitude. Methods. Using 3D magnetohydrodynamic simulations, we modelled the propagation of kink waves in a magnetic flux tube, embedded in a realistic atmosphere with thermal conduction, that starts in the chromosphere and extends into the corona. We drove kink waves at four different frequencies, and determined whether they experienced a cut-off. We then calculated the altitude at which the waves were cut-off, and compared it to the prediction of several analytical models. Results. We show that kink waves indeed experience a cut-off in the transition region, and we identified the analytical model that gives the best predictions. In addition, we show that waves with periods shorter than approximately 500 s can still reach the corona by tunnelling through the transition region, with little to no attenuation of their amplitude. This means that such waves can still propagate from the footpoints of loop, and result in heating in the corona.

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G. Pelouze, T. Doorsselaere, K. Karampelas, et. al.
Tue, 10 Jan 23
66/93

Comments: Accepted for publication in A&A. 8 pages, 7 figures

Parker Solar Probe: Four Years of Discoveries at Solar Cycle Minimum [SSA]

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http://arxiv.org/abs/2301.02727


Launched on 12 Aug. 2018, NASA’s Parker Solar Probe had completed 13 of its scheduled 24 orbits around the Sun by Nov. 2022. The mission’s primary science goal is to determine the structure and dynamics of the Sun’s coronal magnetic field, understand how the solar corona and wind are heated and accelerated, and determine what processes accelerate energetic particles. Parker Solar Probe returned a treasure trove of science data that far exceeded quality, significance, and quantity expectations, leading to a significant number of discoveries reported in nearly 700 peer-reviewed publications. The first four years of the 7-year primary mission duration have been mostly during solar minimum conditions with few major solar events. Starting with orbit 8 (i.e., 28 Apr. 2021), Parker flew through the magnetically dominated corona, i.e., sub-Alfv\’enic solar wind, which is one of the mission’s primary objectives. In this paper, we present an overview of the scientific advances made mainly during the first four years of the Parker Solar Probe mission, which go well beyond the three science objectives that are: (1) Trace the flow of energy that heats and accelerates the solar corona and solar wind; (2) Determine the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind; and (3) Explore mechanisms that accelerate and transport energetic particles.

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N. Raouafi, L. Matteini, J. Squire, et. al.
Tue, 10 Jan 23
67/93

Comments: 157 pages, 65 figures

Spatio-Temporal Comparisons of the Hydrogen-Alpha Line Width and ALMA 3 mm Brightness Temperature in the Weak Solar Network [SSA]

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http://arxiv.org/abs/2301.02725


The strongest known correspondence between ALMA 3mm emission and other solar observations is between the H-alpha line width and 3 mm brightness temperature, while the typical 3-5min p-mode oscillations found in many chromospheric diagnostics are often lacking from ALMA Band 3 and 6 observations. We study these issues using a publicly available data set of weak network flux near disk center at time SOL2017-03-17T15:42-16:45 that includes IBIS H-alpha and ALMA 3 mm data series. We confirm the correlation between the H-alpha line width and the 3 mm temperature, but find a different slope between the two diagnostics for hot versus cool regions, both of which are steeper than previous reports. The origin of the two slopes is unknown, but does hold for the duration of the observations. Spatially averaged power spectra of the IBIS data do show p-mode oscillations while the ALMA data do not. However, removing IBIS data at times corresponding to the ALMA calibration windows makes the averaged power spectra for the two data series nearly identical. Spatial maps of the power integrated over p-mode frequency bands agree well between the two data series and show the typical pattern of magnetic shadows and halos found in many chromospheric diagnostics. We therefore argue that the lack of observed p-modes in the ALMA data may be predominantly due to spectral windowing induced by the timing and duration of the calibration observations.

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L. Tarr, A. Kobelski, S. Jaeggli, et. al.
Tue, 10 Jan 23
77/93

Comments: 25 pages, 12 figures, Accepted for publication in Frontiers in Astronomy and Space Science special topic “The Sun Seen with the Atacama Large mm and sub-mm Array (ALMA) – First Results”

Detecting the heterodyning of gravitational waves [CL]

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http://arxiv.org/abs/2301.02672


Gravitational waves modulate the apparent frequencies of other periodic signals. We propose to use this effect to detect low-frequency gravitational waves by searching for correlated frequency modulations in a large set of well-resolved gravitational wave signals. We apply our proposed method to the large number of gravitational wave signals from Galactic binary white dwarfs that are expected to be detected with the planned space-based gravitational wave detector LISA. We show that, given current projections for the number and properties of these sources and the sensitivity of the instrument, this method would enable the detection of background gravitational wave strain amplitudes of, e.g., $A\simeq10^{-10}$ at a frequency $F\simeq10^{-8}\,\rm Hz$. When using signals from binary neutron stars such as those expected to be observed with proposed detectors like DECIGO, we expect a sensitivity to gravitational waves competitive with that of current Pulsar Timing Arrays. This would allow the detection of gravitational waves from, e.g., super-massive black hole binaries with chirp masses $M_c\gtrsim10^9\,\rm M_\odot$ at a distance $D\simeq10\,\rm Mpc$. Our results show that gravitational-wave detectors could be sensitive at frequencies outside of their designed bandwidth using the same infrastructure. This has the potential to open up unexplored and otherwise inaccessible parts of the gravitational wave spectrum.

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J. Stegmann and S. Vermeulen
Tue, 10 Jan 23
84/93

Comments: 10 pages, 5 figures, 1 table, comments welcome

Hot white dwarfs and pre-white dwarfs discovered with SALT [SSA]

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http://arxiv.org/abs/2301.03550


The Southern African Large Telescope (SALT) survey of helium-rich hot subdwarfs aims to explore evolutionary pathways amongst groups of highly-evolved stars. The selection criteria mean that several hot white dwarfs and related objects have also been included. This paper reports the discovery and analysis of eight new very hot white dwarf and pre-white dwarf stars with effective temperatures exceeding 100,000 K. They include two PG1159 stars, one DO white dwarf, three O(He) and two O(H) stars. One of the O(H) stars is the central star of a newly-discovered planetary nebula, the other is the hottest `naked’ O(H) star. Both of the PG1159 stars are GW Vir variables, one being the hottest GW Vir star measured and a crucial test for pulsation stability models. The DO white dwarf is also the hottest in its class.

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C. Jeffery, K. Werner, D. Kilkenny, et. al.
Tue, 10 Jan 23
85/93

Comments: 10 pages, 13 figures

An APEX study of molecular outflows in FUor-type stars [SSA]

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http://arxiv.org/abs/2301.03387


FU Orionis-type objects (FUors) are low-mass pre-main-sequence objects which go through a short-lived phase (~100 years) of increased mass accretion rate (from 10^-8 to 10^-4 M_sun yr^-1). These eruptive young stars are in the early stages of stellar evolution and, thus, still deeply embedded in a massive envelope that feeds material to the circumstellar disk that is then accreted onto the star. Some FUors drive molecular outflows, i.e. low-velocity wide-angle magneto-hydrodynamical winds, that inject energy and momentum back to the surrounding envelopes, and help clear the material surrounding the young star. Here we present a 12CO (3–2), 13CO (3–2) and 12CO (4–3) survey of 20 FUor-type eruptive young stars observed with APEX. We use our 13CO (3–2) observations to measure the masses of the envelopes surrounding each FUor and find an agreement with the FUor evolutionary trend found from the 10um silicate feature. We find outflows in 11 FUors, calculate their masses and other kinematic properties, and compare these with those of outflows found around quiescent young stellar objects gathered from the literature. This comparison indicates that outflows in FUors are more massive than outflows in quiescent sources, and that FUor outflows have a higher ratio outflow mass with respect to the envelope than the quiescent sample, indicating that the eruptive young stars have lower star-forming efficiencies. Finally, we found that the outflow forces in FUors are similar to those of quiescent young stellar objects, indicating that their accretion histories are similar or that the FUor outflows have lower velocities.

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F. Miera, &. Kóspál, P. Ábrahám, et. al.
Tue, 10 Jan 23
88/93

Comments: Accepted for publication in ApJ. 29 pages, 8 tables, 10 figures, 2 figuresets

Hypothesis of a new fundamental interaction versus the particle oscillation concept [CL]

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http://arxiv.org/abs/2301.03366


The emergence of a logically simple solution to the solar neutrino problem based on the hypothesis of the existence of a new interaction involving electron neutrinos and nucleons did not weaken the dominance of the oscillation concept. Therefore, a significant part of the present work is devoted to proving that the basic elements of this concept either do not correspond to the principles of classical logic, or violate the energy-momentum conservation law, or contradict the quantum mechanical basis of coherence, or represent a primitive falsehood. Our analysis concerns successively all stages of the formation of the concept from its conceiving to the assertion about the conversion of the solar electron neutrino into a muon one. When discussing a new fundamental interaction, we note the decisive role in the outcome of the processes of changing the handedness of a neutrino (antineutrino) at each act of its interaction with a real or virtual massless pseudoscalar boson, due to which, at the exit from the Sun, the fluxes of left- and right-handed electron neutrinos become approximately equal. Thanks to the new interaction, beta decays of nuclei have a mode with the emission of a massless pseudoscalar boson, at which the antineutrino changes its handedness and becomes unobservable, what is the essence of the reactor antineutrino anomaly. The nature of the gallium anomaly is similar.

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L. L.M.Slad
Tue, 10 Jan 23
89/93

Comments: 19 pages

Connecting theory of plasmoid-modulated reconnection to observations of solar flares [SSA]

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http://arxiv.org/abs/2301.03239


The short timescale of the solar flare reconnection process has long proved to be a puzzle. Recent studies suggest the importance of the formation of plasmoids in the reconnecting current sheet, with quantifying the aspect ratio of the width to length of the current sheet in terms of a negative power $\alpha$ of the Lundquist number, i.e. $S^{-\alpha}$, being key to understanding the onset of plasmoids formation. In this paper we make the first application of theoretical scalings for this aspect ratio to observed flares to evaluate how plasmoid formation may connect with observations. We find that for three different flares showing plasmoids a range of $\alpha$ values of $\alpha= 0.27$ to $0.31$. The values in this small range implies that plasmoids may be forming before the theoretically predicted critical aspect ratio ($\alpha=1/3$) has been reached, potentially presenting a challenge for the theoretical models.

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A. Hillier and S. Takasao
Tue, 10 Jan 23
91/93

Comments: 6 pages, 1 figure, 1 table. Published Open Access version (this https URL)

Evolution of the reservoirs of volatiles in the protosolar nebula [EPA]

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http://arxiv.org/abs/2301.02482


The supersolar abundances of volatiles observed in giant planets suggest that a compositional gradient was present at the time of their formation in the protosolar nebula. To explain this gradient, several studies have investigated the radial transport of trace species and the effect of icelines on the abundance profiles of solids and vapors formed in the disk. However, these models only consider the presence of solids in the forms of pure condensates or amorphous ice during the evolution of the protosolar nebula. They usually neglect the possible crystallization and destabilization of clathrates, along with the resulting interplay between the abundance of water and those of these crystalline forms. This study is aimed at pushing this kind of investigation further by considering all possible solid phases together in the protosolar nebula: pure condensates, amorphous ice, and clathrates. To this end, we used a one-dimensional (1D) protoplanetary disk model coupled with modules describing the evolution of trace species in the vapor phase, as well as the dynamics of dust and pebbles. Eleven key species are considered here, including H$_2$O, CO, CO$_2$, CH$_4$, H$_2$S, N$_2$, NH$_3$, Ar, Kr, Xe, and PH$_3$. Two sets of initial conditions are explored for the protosolar nebula. In a first scenario, the disk is initially filled with icy grains in the forms of pure condensates. In this case, we show that clathrates can crystallize and form enrichment peaks up to about ten times the initial abundances at their crystallization lines. In a second scenario, the volatiles were delivered to the protosolar nebula in the forms of amorphous grains. In this case, the presence of clathrates is not possible because there is no available crystalline water ice in their formation region. Enrichment peaks of pure condensates also form beyond the snowline up to about seven times the initial abundances.

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A. Schneeberger, O. Mousis, A. Aguichine, et. al.
Mon, 9 Jan 23
3/59

Comments: To be published in Astronomy & Astrophysics 19 pages, 11 figures

What does a typical full-disc around a post-AGB binary look like? — Radiative transfer models reproducing PIONIER, GRAVITY, and MATISSE data [SSA]

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http://arxiv.org/abs/2301.02622


(abridged) Stable circumbinary discs around evolved post-Asymptotic Giant branch (post-AGB) binary systems show many similarities with protoplanetary discs around young stellar objects. These discs can provide constraints on both binary evolution and the formation of macrostructures within circumstellar discs. Here we focus on one post-AGB binary system: IRAS08544-4431. We aim to refine the physical model of IRAS08544-4431 with a radiative transfer treatment and continue the near-infrared and mid-infrared interferometric analysis covering the H-, K-, L-, and N-bands. We aim to capture the previously detected amount of over-resolved flux and the radial intensity profile at and beyond the inner dust disc rim to put constraints on the physical processes in the inner disc regions. We used a Monte Carlo radiative transfer code to investigate the physical structure of the disc by reproducing both the photometry and the multi-wavelength infrared interferometric data set. We developed a strategy to identify the models which perform best to reproduce our data set. We found a family of models that successfully fit the infrared photometric and interferometric data in all bands. Some over-resolved flux component was recovered in all bands but the optimised models still fall short to explain all the over-resolved flux. This suggests that another dusty structure within the system plays a role. Multi-wavelength infrared interferometric observations of circumstellar discs allow to study the inner disc regions in unprecedented detail. The refined physical models can reproduce most of the investigated features, including the photometric characteristics, the radial extent, and the overall shape of the visibility curves. Our multi-wavelength interferometric observations combined with photometry show that the disc is similar to protoplanetary discs with similar dust masses and efficient dust growth.

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A. Corporaal, J. Kluska, H. Winckel, et. al.
Mon, 9 Jan 23
7/59

Comments: 18 pages, 13 figures (including apppendix), accepted for publication in A&A

Role of small-scale impulsive events in heating the X-ray bright points of the quiet Sun [SSA]

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http://arxiv.org/abs/2301.02519


Small-scale impulsive events, known as nanoflares, are thought to be one of the prime candidates that can keep the solar corona hot at its multi-million Kelvin temperature. Individual nanoflares are difficult to detect with the current generation instruments; however, their presence can be inferred through indirect techniques such as a Differential Emission Measure (DEM) analysis. Here we employ this technique to investigate the possibility of nanoflare heating of the quiet corona during the minimum of solar cycle 24. During this minimum, active regions (ARs) were absent on the solar-disk for extended periods. In the absence of ARs, X-ray bright points (XBP) are the dominant contributor to disk-integrated X-rays. We estimate the DEM of the XBPs using observations from the Solar X-ray Monitor (XSM) onboard the Chandrayaan-2 orbiter and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamic Observatory. XBPs consist of small-scale loops associated with bipolar magnetic fields. We simulate such XBP loops using the EBTEL hydrodynamic code. The lengths and magnetic field strengths of these loops are obtained through a potential field extrapolation of the photospheric magnetogram. Each loop is assumed to be heated by random nanoflares having an energy that depends on the loop properties. The composite nanoflare energy distribution for all the loops has a power-law slope close to -2.5. The simulation output is then used to obtain the integrated DEM. It agrees remarkably well with the observed DEM at temperatures above 1 MK, suggesting that the nanoflare distribution, as predicted by our model, can explain the XBP heating.

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B. Mondal, J. Klimchuk, S. Vadawale, et. al.
Mon, 9 Jan 23
12/59

Comments: Submitted in the Astrophysical Journal, 20 pages, 10 figures

Oscillatory reconnection as a plasma diagnostic in the solar corona [SSA]

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http://arxiv.org/abs/2301.02452


Oscillatory reconnection is a relaxation process in magnetised plasma, with an inherent periodicity that is exclusively dependent on the properties of the background plasma. This study focuses on the seismological prospects of oscillatory reconnection in the solar corona. We perform three sets of parameter studies (for characteristic coronal values of the background magnetic field, density and temperature) using the PLUTO code to solve the fully compressive, resistive MHD equations for a 2D magnetic X-point. From each parameter study, we derive the period of the oscillatory reconnection. We find that this period is inversely proportional to the characteristic strength of the background magnetic field and the square root of the initial plasma temperature, while following a square root dependency upon the equilibrium plasma density. These results reveal an inverse proportionality between the magnitude of the Alfv\’en speed and the period, as well as the background sound speed and the period. Furthermore, we note that the addition of anisotropic thermal conduction only leads to a small increase in the mean value for the period. Finally, we establish an empirical formula that gives the value for the period in relation to the background magnetic field, density and temperature. This gives us a quantified relation for oscillatory reconnection, to be used as a plasma diagnostic in the solar corona, opening up the possibility of using oscillatory reconnection for coronal seismology.

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K. Karampelas, J. McLaughlin, G. Botha, et. al.
Mon, 9 Jan 23
15/59

Comments: 16 pages, 10 figures, accepted for publication in ApJ

Reconstruction of the Sunspot Number Source Database and the 1947 Zurich Discontinuity [SSA]

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http://arxiv.org/abs/2301.02429


The recalibration of the sunspot number series, the primary long-term record of the solar cycle, requires the recovery of the entire collection of raw sunspot counts collected by the Zurich Observatory for the production of this index between 1849 and 1980. Here, we report about the major progresses accomplished recently in the construction of this global digital sunspot number database, and we derive global statistics of all the individual observers and professional observatories who provided sunspot data over more than 130 years. First, we can announce the full recovery of long-lost source-data tables covering the last 34 years between 1945 and 1979, and we describe the unique information available in those tables. We then also retrace the evolution of the core observing team in Zurich and of the auxiliary stations. In 1947, we find a major disruption in the composition of both the Zurich team and the international network of auxiliary stations. This sharp transition is unique in the history of the Zurich Observatory and coincides with the main scale-jump found in the original Zurich sunspot number series, the so-called “Waldmeier” jump. This adds key historical evidence explaining why methodological changes introduced progressively in the early $20^{th}$ century could play a role precisely at that time. We conclude on the remaining steps needed to fully complete this new sunspot data resource.

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F. Clette, L. Lefèvre, S. Bechet, et. al.
Mon, 9 Jan 23
19/59

Comments: 22 pages, 9 figures

Photometric variable stars in the young open cluster NGC 6823 [SSA]

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http://arxiv.org/abs/2301.02399


We present stellar variability towards the young open cluster NGC\,6823. Time series $V$- and $I$-band CCD photometry led to identification and characterization of 88 variable stars, of which only 14 have been previously recognized. We ascertain the membership of each variable with optical $UBVI$ and infrared photometry, and with Gaia EDR3 parallax and proper motion data. Seventy two variable stars are found to be cluster members, of which 25 are main sequence stars and 48 are pre-main-sequence stars. The probable cluster members collectively suggest an isochrone age of the cluster to be about 2~Myrs based on the GAIA photometry. With the color and magnitude, as well as the shape of the light curve, we have classified the main sequence variables into $\beta$~Cep, $\delta$~Scuti, slowly pulsating B type, and new class variables. Among the pre-main-sequence variables, eight are classical T Tauri variables, and four are Herbig Ae/Be objects, whereas the remaining belong to the weak-lined T Tauri population. The variable nature of 32 stars is validated with TESS light curves. Our work provides refined classification of variability of pre-main-sequence and main-sequence cluster members of the active star-forming complex, Sharpless\,86. Despite no strong evidence of the disk-locking mechanism in the present sample of TTSs, one TTS with larger $\Delta(I-K)$ is found to be slow rotator.

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S. Lata, W. Chen, J. Pandey, et. al.
Mon, 9 Jan 23
20/59

Comments: 19 pages, 19 figures, accepted for publication in MNRAS

The Pristine survey — XX: GTC follow-up observations of extremely metal-poor stars identified from Pristine and LAMOST [GA]

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http://arxiv.org/abs/2301.02265


Ultra metal-poor stars ([Fe/H] < -4.0) are very rare, and finding them is a challenging task. Both narrow-band photometry and low-resolution spectroscopy have been useful tools for identifying candidates, and in this work we combine both approaches. We cross-matched metallicity-sensitive photometry from the Pristine survey with the low-resolution spectroscopic LAMOST database, and re-analysed all LAMOST spectra with [Fe/H]_Pristine < -2.5. We find that ~1/3rd of this sample (selected without [Fe/H]_Pristine quality cuts) also have spectroscopic [Fe/H] < -2.5. From this sample, containing many low signal-to-noise (S/N) spectra, we selected eleven stars potentially having [Fe/H] < -4.0 or [Fe/H] < -3.0 with very high carbon abundances, and we performed higher S/N medium-resolution spectroscopic follow-up with OSIRIS on the 10.4m Gran Telescopio Canarias (GTC). We confirm their extremely low metallicities, with a mean of [Fe/H] = -3.4 and the most metal-poor star having [Fe/H]= -3.8. Three of these are clearly carbon-enhanced metal-poor (CEMP) stars with +1.65 < [C/Fe] < +2.45. The two most carbon-rich stars are either among the most metal-poor CEMP-s stars or the most carbon-rich CEMP-no stars known, the third is likely a CEMP-no star. We derived orbital properties for the OSIRIS sample and find that only one of our targets can be confidently associated with known substructures/accretion events, and that three out of four inner halo stars have prograde orbits. Large spectroscopic surveys may contain many hidden extremely and ultra metal-poor stars, and adding additional information from e.g. photometry as in this work can uncover them more efficiently and confidently.

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A. Arentsen, D. Aguado, F. Sestito, et. al.
Mon, 9 Jan 23
22/59

Comments: 13 pages, accepted for publication in MNRAS

The study of eleven contact binaries with mass ratios less than 0.1 [SSA]

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http://arxiv.org/abs/2301.02471


Multi-band photometric observations of eleven totally eclipsing contact binaries were carried out. Applying the Wilson-Devinney program, photometric solutions were obtained. There are two W-subtype systems, which are CRTS J133031.1+161202 and CRTS J154254.0+324652, and the rest systems are A-subtype systems. CRTS J154254.0+324652 has the highest fill-out factor with 94.3$\%$, and the lowest object is CRTS J155009.2+493639 with only 18.9$\%$. The mass ratios of the eleven systems are all less than 0.1, which means that they are extremely low mass ratio binary systems. We performed period variation investigation and found that the orbital periods of three systems decrease slowly, which may be caused by the angular momentum loss, and of six systems increase slowly, which indicates that the materials may transfer from the secondary component to the primary component. LAMOST low$-$resolution spectra of four objects were analyzed, and using the spectral subtraction technique, H$\alpha$ emission line was detected, which means that the four objects exhibit chromospheric activity. In order to understand their evolutionary status, the mass-luminosity and mass-radius diagrams were plotted. The two diagrams indicate that the primary component is in the main sequence evolution stage, and the secondary component is above TAMS, indicating that they are over-luminous. To determine whether the eleven systems are in stable state, the ratio of spin angular momentum to orbital angular momentum ($J_{s}/J_{o}$) and the instability parameters were calculated, and we argued that CRTS J234634.7+222824 is on the verge of a merger.

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X. Liu, K. Li, R. Michel, et. al.
Mon, 9 Jan 23
23/59

Comments: 16 pages, 6 figures, and 11 tables, accepted by MNRAS

Forbidden emission lines in protostellar outflows and jets with MUSE [SSA]

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http://arxiv.org/abs/2301.02559


Forbidden emission lines in protoplanetary disks are a key diagnostic in studies of the evolution of the disk and the host star. We report spatially resolved emission lines, [OI] 6300, 6363, [NII] 6548, 6583, H$\alpha$, and [SII] 6716, 6730 Angstrom that are believed to be associated with jets and magnetically driven winds in the inner disks. Observations were carried out with the optical integral field spectrograph of the Multi Unit Spectroscopic Explorer (MUSE), at the Very Large Telescope (VLT). With a resolution of 0.025 X 0.025 arcsec$^{2}$, we aim to derive the position angle of the outflow/jet (PA${outflow/jet}$) that is connected with the inner disk. The forbidden emission lines analyzed here have their origin at the inner parts of the protoplanetary disk. From the maximum intensity emission along the outflow/jet in DL Tau, CI Tau, DS Tau, IP Tau, and IM Lup, we were able to reliably measure the PA${outflow/jet}$ for most of the identified lines. We found that our estimates agree with PA${dust}$ for most of the disks. These estimates depend on the signal-to-noise level and the collimation of the outflow (jet). The outflows/jets in CIDA 9, GO Tau, and GW Lup are too compact for a PA${outflow/jet}$ to be estimated. Based on our kinematics analysis, we confirm that DL Tau and CI Tau host a strong outflow/jet with line-of-sight velocities much greater than 100 km s$^{-1}$, whereas DS Tau, IP Tau, and IM Lup velocities are lower and their structures encompass low-velocity components to be more associated with winds. Our estimates for the mass-loss rate, $\dot{M}{{loss}}$, range between (1.1-6.5)X10$^{-7}$-10$^{-8}$ $M{\odot}$ yr$^{-1}$ for the disk-outflow/jet systems analyzed here. The outflow/jet systems analyzed here are aligned within around 1 degree between the inner and outer disk. Further observations are needed to confirm a potential misalignment in IM Lup.

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L. Flores-Rivera, M. Flock, N. Kurtovic, et. al.
Mon, 9 Jan 23
26/59

Comments: Accepted on December 19 2022

The $\textit{Gaia}$ view of the Cepheus OB2 association [SSA]

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http://arxiv.org/abs/2301.02346


OB associations, birthplaces of the most luminous stars, are key objects for understanding the formation of high-mass stars and their effects on their environments. The aim of this work is to explore the structure and kinematics of the Cepheus OB2 association and characterize the history of star formation in the region — in particular, the role of the Cepheus Bubble, surrounding Cepheus OB2. Based on \gaia\ DR3 data we study the spatial and age distribution and kinematics of young stars in the region. We select candidate pre-main-sequence stars in the $M_\mathrm{G}$ vs. \gbp$-$\grp\ colour-magnitude diagram, and using a clustering algorithm, we identify 13 stellar groups belonging to Cep OB2. Four groups, consisting of 10-13 Myr old low- and intermediate-mass stars, are located in the interior of the bubble, and are part of the oldest subsystem of the association Cep OB2a. Younger groups are found on the periphery. The tangential velocities suggest that some groups on the periphery were born in an expanding system of star-forming clouds, whereas others have been formed due to the collision of their parent cloud with the expanding bubble.

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M. Szilágyi, M. Kun, P. Ábrahám, et. al.
Mon, 9 Jan 23
28/59

Comments: Accepted in MNRAS, 17 pages, 17 figures

Is the $F_{10.7cm}$ — Sunspot Number relation linear and stable ? [SSA]

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http://arxiv.org/abs/2301.02588


The $F_{10.7cm}$ radio flux and the Sunspot Number are the most widely used long-term indices of solar activity. They are strongly correlated, which led to the publication of many proxy relations allowing to convert one index onto the other. However, those existing proxies show significant disagreements, in particular at low solar activity. Our aim is to bring a global clarification of those many issues. We compute new polynomial regressions up to degree 4, in order to obtain a more accurate proxy. We also study the role of temporal averaging on the regression, and we investigate the issue of the all-quiet $F_{10.7}$ background flux. Finally, we check for any change in the $F_{10.7}$ — sunspot number relation over the entire period 1947 — 2015. We find that, with a $4^{th}$-degree polynomial, we obtain a more accurate proxy relation than all previous published ones, and we derive a formula giving standard errors. The relation is different for daily, monthly and yearly mean values, and it proves to be fully linear for raw non-averaged daily data. By a simple two-component model for daily values, we show how temporal averaging leads to non-linear proxy relations. We also show that the quiet-Sun $F_{10.7}$ background is not absolute and actually depends on the duration of the spotless periods. Finally, we find that the $F_{10.7cm}$ time series is inhomogeneous, with an abrupt 10.5% upward jump occurring between 1980 and 1981. Our new proxy relations show the importance of temporal scale for choosing the appropriate proxy and the $F_{10.7}$ quiet-Sun background level. From historical evidence, we conclude that the 1981 jump is most likely due to a unique change in the $F_{10.7}$ scientific team and the data processing, and that the newly re-calibrated sunspot number (version2) will probably provide the only possible reference to correct this inhomogeneity.

Read this paper on arXiv…

F. Clette
Mon, 9 Jan 23
30/59

Comments: 51 pages, 27 figures, 10 tables

Redder than Red: Discovery of an Exceptionally Red L/T Transition Dwarf [SSA]

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http://arxiv.org/abs/2301.02322


We present the discovery of CWISE J050626.96$+$073842.4 (CWISE J0506$+$0738), an L/T transition dwarf with extremely red near-infrared colors discovered through the Backyard Worlds: Planet 9 citizen science project. Photometry from UKIRT and CatWISE give a $(J-K){\rm MKO}$ color of 2.97$\pm$0.03 mag and a $J{\rm MKO}-$W2 color of 4.93$\pm$0.02 mag, making CWISE J0506$+$0738 the reddest known free-floating L/T dwarf in both colors. We confirm the extremely red nature of CWISE J0506$+$0738 using Keck/NIRES near-infrared spectroscopy and establish that it is a low-gravity late-type L/T transition dwarf. The spectrum of CWISE J0506$+$0738 shows possible signatures of CH$_4$ absorption in its atmosphere, suggesting a colder effective temperature than other known, young, red L dwarfs. We assign a preliminary spectral type for this source of L8$\gamma$-T0$\gamma$. We tentatively find that CWISE J0506$+$0738 is variable at 3-5 $\mu$m based on multi-epoch WISE photometry. Proper motions derived from follow-up UKIRT observations combined with a radial velocity from our Keck/NIRES spectrum and a photometric distance estimate indicate a strong membership probability in the $\beta$ Pic moving group. A future parallax measurement will help to establish a more definitive moving group membership for this unusual object.

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A. Schneider, A. Burgasser, J. Bruursema, et. al.
Mon, 9 Jan 23
31/59

Comments: Accepted to ApJ Letters

Formation of Magnetic Switchbacks Observed by Parker Solar Probe [SSA]

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http://arxiv.org/abs/2301.02572


Magnetic switchbacks are rapid high amplitude reversals of the radial magnetic field in the solar wind that do not involve a heliospheric current sheet crossing. First seen sporadically in the seventies in Mariner and Helios data, switchbacks were later observed by the Ulysses spacecraft beyond 1 au and have been recently identified as a typical component of solar wind fluctuations in the inner heliosphere by the Parker Solar Probe spacecraft. Here we provide a simple yet predictive theory for the formation of these magnetic reversals: the switchbacks are produced by the shear of circularly polarized Alfv\’en waves by a transversely varying radial wave propagation velocity. We provide an analytic expression for the magnetic field variation, establish the necessary and sufficient conditions and show that the mechanism works in a realistic solar wind scenario.

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G. Toth, M. Velli and B. Holst
Mon, 9 Jan 23
39/59

Comments: Submitted to Nature

The CARMENES search for exoplanets around M dwarfs, Wolf 1069 b: Earth-mass planet in the habitable zone of a nearby, very low-mass star [EPA]

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http://arxiv.org/abs/2301.02477


We present the discovery of an Earth-mass planet ($M_b\sin i = 1.36\pm0.21M_\oplus$) on a 15.6d orbit of a relatively nearby ($d\sim$9.6pc) and low-mass ($0.167\pm0.011 M_\odot$) M5.0V star, Wolf 1069. Sitting at a separation of $0.0672\pm0.0014$au away from the host star puts Wolf 1069b in the habitable zone (HZ), receiving an incident flux of $S=0.652\pm0.029S_\oplus$. The planetary signal was detected using telluric-corrected radial-velocity (RV) data from the CARMENES spectrograph, amounting to a total of 262 spectroscopic observations covering almost four years. There are additional long-period signals in the RVs, one of which we attribute to the stellar rotation period. This is possible thanks to our photometric analysis including new, well-sampled monitoring campaigns undergone with the OSN and TJO facilities that supplement archival photometry (i.e., from MEarth and SuperWASP), and this yielded an updated rotational period range of $P_{rot}=150-170$d, with a likely value at $169.3^{+3.7}_{-3.6}$d. The stellar activity indicators provided by the CARMENES spectra likewise demonstrate evidence for the slow rotation period, though not as accurately due to possible factors such as signal aliasing or spot evolution. Our detectability limits indicate that additional planets more massive than one Earth mass with orbital periods of less than 10 days can be ruled out, suggesting that perhaps Wolf 1069 b had a violent formation history. This planet is also the 6th closest Earth-mass planet situated in the conservative HZ, after Proxima Centauri b, GJ 1061d, Teegarden’s Star c, and GJ 1002 b and c. Despite not transiting, Wolf 1069b is nonetheless a very promising target for future three-dimensional climate models to investigate various habitability cases as well as for sub-ms$^{-1}$ RV campaigns to search for potential inner sub-Earth-mass planets in order to test planet formation theories.

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D. Kossakowski, M. Kürster, T. Trifonov, et. al.
Mon, 9 Jan 23
43/59

Comments: 26 pages, 15 figures

A study of convective core overshooting as a function of stellar mass based on two-dimensional hydrodynamical simulations [SSA]

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http://arxiv.org/abs/2301.02604


We perform two-dimensional numerical simulations of core convection for zero-age-main-sequence stars covering a mass range from 3 $M_\odot$ to 20 $M_\odot$. The simulations are performed with the fully compressible time-implicit code MUSIC. We study the efficiency of overshooting, which describes the ballistic process of convective flows crossing a convective boundary, as a function of stellar mass and luminosity. We also study the impact of artificially increasing the stellar luminosity for 3 $M_\odot$ models. The simulations cover hundreds to thousands of convective turnover timescales. Applying the framework of extreme plume events previously developed for convective envelopes, we derive overshooting lengths as a function of stellar masses. We find that the overshooting distance ($d_{\rm ov}$) scales with the stellar luminosity ($L$) and the convective core radius ($r_{\rm conv}$). We derive a scaling law $d_{\rm ov} \propto L^{1/3} r_{\rm conv}^{1/2}$ which is implemented in a 1D stellar evolution code and the resulting stellar models are compared to observations. The scaling predicts values for the overshooting distance that significantly increase with stellar mass, in qualitative agreement with observations. Quantitatively, however, the predicted values are underestimated for masses $\gtrsim 10 M_\odot$. Our 2D simulations show the formation of a nearly-adiabatic layer just above the Schwarzschild boundary of the convective core, as exhibited in recent 3D simulations of convection. The most luminous models show a growth in size with time of the nearly-adiabatic layer. This growth seems to slow down as the upper edge of the nearly-adiabatic layer gets closer to the maximum overshooting length and as the simulation time exceeds the typical thermal diffusive timescale in the overshooting layer.

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I. Baraffe, J. Clarke, A. Morison, et. al.
Mon, 9 Jan 23
44/59

Comments: 13 pages, accepted for publication in MNRAS

New insights on the near-infrared veiling of young stars using CFHT/SPIRou data [SSA]

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http://arxiv.org/abs/2301.02450


Veiling is ubiquitous at different wavelength ranges in accreting stars. However, the origin of the veiling in the IR domain is not well understood. The accretion spot alone is not enough to explain the shallow photospheric IR lines in accreting systems, suggesting that another source is contributing to the veiling in the NIR. The inner disk is often quoted as the additional emitting source meant to explain the IR veiling. In this work, we aim to measure and discuss the NIR veiling to understand its origins and variability timescale, using a sample of 14 accreting stars observed with the CFHT/SPIRou spectrograph, within the framework of the SPIRou Legacy Survey. We compared the veiling measurements with accretion and inner disk diagnostics. The measured veiling grows from the Y to the K band for most of the targets in our sample. The IR veiling agrees with NIR emission excess obtained using photometric data. However, we also find a linear correlation between the veiling and the accretion properties of the system, showing that accretion contributes to the inner disk heating and, consequently, to the inner disk emission excess. We also show a connection between the NIR veiling and the system’s inclination with respect to our line of sight. This is probably due to the reduction of the visible part of the inner disk edge, where the NIR emission excess is expected to arise, as the inclination of the system increases. The NIR veiling appears variable on a timescale of a day, showing the night-by-night dynamics of the optical veiling variability. In the long term, the mean NIR veiling seems to be stable for most of the targets on timescales of a month to a few years. However, during occasional episodes of high accretion, which affect the system’s dynamic, the veiling also seems to be much more prominent at such times, as we found in the case of the target RU Lup.

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A. Sousa, J. Bouvier, S. Alencar, et. al.
Mon, 9 Jan 23
45/59

Comments: N/A

WIYN Open Cluster Study. LXXXVII. HST Ultraviolet Detection of Hot White Dwarf Companions to Blue Lurkers in M67 [SSA]

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http://arxiv.org/abs/2301.02303


We present the results of our Hubble Space Telescope far-ultraviolet survey of the blue lurkers (BLs) in M67. We find evidence for two white dwarf companions among the BLs that are indicative of mass transfer from an evolved companion, one in WOCS 14020 and the other in WOCS 3001. The cooling ages of the white dwarfs suggest that mass transfer in these systems occurred $\sim$300–540 Myr and $\sim$600–900 Myr ago, respectively. The rotation periods and cooling ages of the BLs are consistent with spin-up and subsequent single-star spin-down models, and binary evolution models yield plausible evolutionary pathways to both BLs via highly non-conservative mass transfer. We conclude that the BLs are lower-luminosity analogues to the classical blue stragglers.

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A. Nine, R. Mathieu, N. Gosnell, et. al.
Mon, 9 Jan 23
47/59

Comments: 16 pages, 8 figures. Accepted to ApJ

Re-parameterisation of four limb darkening laws and their implementation into the JKTEBOP code [SSA]

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http://arxiv.org/abs/2301.02531


Limb darkening (LD) is typically parameterised using a range of functional “laws” in models of the light curves of eclipsing binary and transiting planetary systems. The two-coefficient LD laws all suffer from a strong correlation between their coefficients, preventing a reliable determination of both coefficients from high-quality light curves. We use numerical simulations to propose re-parameterisations of the quadratic, logarithmic, square-root and cubic LD laws that show much weaker correlations, and implement them into the JKTEBOP code. We recommend that these re-parameterisations are used whenever both LD coefficients are fitted. Conversely, when fitting for only one coefficient, the standard laws should be used to avoid problems with fixing coefficients at poor values. We find that these choices have little effect on the other fitted parameters of a light curve model. We also recommend that the power-2 LD law should be used as default because it provides a good fit to theoretical predictions, and that the quadratic and linear laws should be avoided because they do not.

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J. Southworth
Mon, 9 Jan 23
50/59

Comments: Accepted for publication in The Observatory. 14 pages, 4 tables, 4 black/white figures

Microphysically modified magnetosonic modes in collisionless, high-$β$ plasmas [HEAP]

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http://arxiv.org/abs/2301.02273


With the support of hybrid-kinetic simulations and analytic theory, we describe the nonlinear behaviour of long-wavelength non-propagating (NP) modes and fast magnetosonic waves in high-$\beta$ collisionless plasmas, with particular attention to their excitation of, and reaction to, kinetic micro-instabilities. The perpendicularly pressure balanced polarization of NP modes produces an excess of perpendicular pressure over parallel pressure in regions where the plasma $\beta$ is increased. For mode amplitudes $\delta B/B_0 \gtrsim 0.3$, this excess excites the mirror instability. Particle scattering off these micro-scale mirrors frustrates the nonlinear saturation of transit-time damping, ensuring that large-amplitude NP modes continue their decay to small amplitudes. At asymptotically large wavelengths, we predict that the mirror-induced scattering will be large enough to interrupt transit-time damping entirely, isotropizing the pressure perturbations and morphing the collisionless NP mode into the magnetohydrodynamic (MHD) entropy mode. In fast waves, a fluctuating pressure anisotropy drives both mirror and firehose instabilities when the wave amplitude satisfies $\delta B/B_0 \gtrsim 2\beta^{-1}$. The induced particle scattering leads to delayed shock formation and MHD-like wave dynamics. Taken alongside prior work on self-interrupting Alfv\’en waves and self-sustaining ion-acoustic waves, our results establish a foundation for new theories of electromagnetic turbulence in low-collisionality, high-$\beta$ plasmas such as the intracluster medium, radiatively inefficient accretion flows, and the near-Earth solar wind.

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S. Majeski, M. Kunz and J. Squire
Mon, 9 Jan 23
58/59

Comments: 44 pages, 21 figures, submitted to Journal of Plasma Physics

Origin of Multifractality in Solar Wind Turbulence: the Role of Current Sheets [SSA]

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http://arxiv.org/abs/2301.02118


In this work, a multifractal framework is proposed to investigate the effects of current sheets in solar wind turbulence. By using multifractal detrended fluctuation analysis coupled with surrogate methods and volatility, two solar wind magnetic field time series are investigated, one with current sheets and one without current sheets. Despite the lack of extreme-events intermittent bursts in the current sheet-free series, both series are shown to be strongly multifractal, although the current sheet-free series displays an almost linear behavior for the scaling exponent of structure functions. Long-range correlations are shown to be the main source of multifractality for the series without current sheets, while a combination of heavy-tail distribution and nonlinear correlations are responsible for multifractality in the series with current sheets. The multifractality in both time series is formally shown to be associated with an energy-cascade process using the p-model.

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L. Gomes, T. Gomes, E. Rempel, et. al.
Fri, 6 Jan 23
3/55

Comments: Accepted by MNRAS

The HH 24 Complex: Jets, Multiple Star Formation, and Orphaned Protostars [SSA]

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http://arxiv.org/abs/2301.01813


The HH 24 complex harbors five collimated jets emanating from a small protostellar multiple system. We have carried out a multi-wavelength study of the jets, their driving sources, and the cloud core hosting the embedded stellar system, based on data from the HST, Gemini, Subaru, APO 3.5m, VLA, and ALMA telescopes. The data show that the multiple system, SSV 63, contains at least 7 sources, ranging in mass from the hydrogen-burning limit to proto-Herbig Ae stars. The stars are in an unstable non-hierarchical configuration, and one member, a borderline brown dwarf, is moving away from the protostellar system with 25 km/s, after being ejected about 5,800 yr ago as an orphaned protostar. Five of the embedded sources are surrounded by small, possibly truncated, disks resolved at 1.3 mm with ALMA. Proper motions and radial velocities imply jet speeds of 200-300 km/s. The two main HH 24 jets, E and C, form a bipolar jet system which traces the innermost portions of parsec-scale chains of Herbig-Haro and H2 shocks with a total extent of at least 3 parsec. H2CO and C18O observations show that the core has been churned and continuously fed by an infalling streamer. 13CO and 12CO trace compact, low-velocity, cavity walls carved by the jets and an ultra-compact molecular outflow from the most embedded object. Chaotic N-body dynamics likely will eject several more of these objects. The ejection of stars from their feeding zones sets their masses. Dynamical decay of non-hierarchical systems can thus be a major contributor to establishing the initial mass function.

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B. Reipurth, J. Bally, H. Yen, et. al.
Fri, 6 Jan 23
5/55

Comments: 57 pages, 61 figures, 12 tables; accepted to Astron.J

White dwarf — red giant star binaries as Type Ia supernova progenitors: with and without magnetic confinement [HEAP]

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http://arxiv.org/abs/2301.01783


Various white-dwarf (WD) binary scenarios have been proposed trying to understand the nature and the diversity of Type Ia supernovae (SNe Ia). In this work, we study the evolution of carbon-oxygen WD — red giant (RG) binaries (including the role of magnetic confinement) as possible SN Ia progenitors (the so-called symbiotic progenitor channel). Using the \textsc{mesa} stellar evolution code, we calculate the time dependence of the structure of the RG star, the wind mass loss, the Roche-lobe-overflow (RLOF) mass-transfer rate, the polar mass-accretion rate (in the case of magnetic confinement), and the orbital and angular-momentum evolution. We consider cases where the WD is non-magnetic and cases where the magnetic field is strong enough to force accretion onto the two small polar caps of the WD. Confined accretion onto a small area allows for more efficient hydrogen burning, potentially suppressing nova outbursts. This makes it easier for the WD to grow in mass towards the Chandrasekhar mass limit and explode as a SN Ia. With magnetic confinement, the initial parameter space of the symbiotic channel for SNe Ia is shifted towards shorter orbital periods and lower donor masses compared to the case without magnetic confinement. Searches for low-mass He WDs or relatively low-mass giants with partially stripped envelopes that survived the supernova explosion and are found in SN remnants will provide crucial insights for our understanding of the contribution of this symbiotic channel.

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I. Ablimit, P. Podsiadlowski, R. Stefano, et. al.
Fri, 6 Jan 23
11/55

Comments: Published in The Astrophysical Journal Letters (published 2022 December 22)

The VLT/SPHERE view of the ATOMIUM cool evolved star sample. I. Overview: Sample characterization through polarization analysis [SSA]

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http://arxiv.org/abs/2301.02081


Aims. Through the ATOMIUM project, based on an ALMA large program, we aim to present a consistent view of a sample of 17 nearby cool evolved stars (Aymptotic Giant Branch and red supergiant stars).
Methods. Here we present VLT/SPHERE-ZIMPOL polarimetric maps obtained in the visible of 14 out of the 17 ATOMIUM sources. They were obtained contemporaneously with the ALMA high spatial resolution data. To help interpret the polarized signal, we produced synthetic maps of light scattering by dust, through 3D radiative transfer simulations with the RADMC3D code.
Results. The degree of linear polarization (DoLP) observed by ZIMPOL spreads across several optical filters. We infer that it primarily probes dust located just outside of the point spread function, and in or near the plane of the sky, with a total optical depth close to unity in the line of sight, representing only a fraction of the total circumstellar dust. The maximum DoLP ranges from 0.03-0.38 depending on the source, fractions that can be reproduced by our 3D pilot models for grains composed of common dust species. The spatial structure of the DoLP shows a diverse set of shapes. Only for three sources do we note a correlation between the ALMA CO and SiO lines, which trace the gas density, and the DoLP, which traces the dust.
Conclusion. The clumpiness of the DoLP and the lack of a consistent correlation between the gas and the dust location show that, in the inner circumstellar environment (CSE), dust formation occurs at very specific sites. This has potential consequences for the derived mass-loss rates and dust-to-gas ratio in the inner region of the CSE. Except for $\pi^1$~Gru and perhaps GY Aql, we do not detect interactions between the circumstellar wind and the hypothesized companions that shape the wind at larger scales. This suggests that the orbits of any other companions are tilted out of the plane of the sky.

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M. Montargès, E. Cannon, A. Koter, et. al.
Fri, 6 Jan 23
16/55

Comments: Accepted for publication in Astronomy & Astrophysics. 22 pages, 15 figures, 5 tables

Temperature of Solar Orbiter/EUI quiet Sun small scale brightenings: evidence for a cooler component [SSA]

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http://arxiv.org/abs/2301.02040


Context: On 2020 May 30, small and short-lived EUV brightenings were observed in the Quiet Sun (QS) during a four minutes sequence by EUI/HRIEUV on board Solar Orbiter. Their physical origin and possible impact on coronal or Transition Region (TR) heating are still to be determined. Aims: Our aim is to derive the statistical thermal evolution of these events in order to establish their coronal or TR origin. Methods. Our thermal analysis takes advantage of the multithermal sensitivity of the Atmospheric Imaging Assembly (AIA) imager on board the Solar Dynamics Observatory (SDO). We first identified these HRIEUV events in the six coronal bands of AIA. We then performed a statistical time lag analysis, which quantifies the delays between the light curves from different bands. These time lags can give significant insights into the temperature evolution of these events. The analysis is performed taking into account the possible contribution to the results from the background and foreground emissions. Results: The events are characterized by time lags inferior to the AIA cadence of 12 s, for all nine couples of AIA bands analyzed. Our interpretation is the possible co-presence of events which reach or do not reach coronal temperatures ($\approx$ 1MK). We believe that the cool population dominates the events analyzed in this work.

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A. Dolliou, S. Parenti, F. Auchère, et. al.
Fri, 6 Jan 23
19/55

Comments: 14 pages, 8 figures

The temperature dependency of Wolf-Rayet-type mass loss: An exploratory study for winds launched by the hot iron bump [SSA]

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http://arxiv.org/abs/2301.01785


CONTEXT: The mass loss of He-burning stars, which are partially or completely stripped of their outer hydrogen envelope, is a catalyst of the cosmic matter cycle and decisive ingredient of massive star evolution. Yet, its theoretical fundament is only starting to emerge with major dependencies still to be uncovered.
AIMS: A temperature or radius dependence is usually not included in descriptions for the mass loss of classical Wolf-Rayet (cWR) stars, despite being crucial for other hot star wind domains. We thus aim to determine whether such a dependency will also be necessary for a comprehensive description of mass loss in the cWR regime.
METHODS: Sequences of dynamically consistent atmosphere models were calculated with the hydrodynamic branch of the PoWR code along the temperature domain, using different choices for luminosity, mass, and surface abundances. For the first time, we allowed nonmonotonic velocity fields when solving the equation of motion. The resulting velocity structures were then interpolated for the comoving-frame radiative transfer, ensuring that the main wind characteristics were preserved.
RESULTS: We find a strong dependence of the mass-loss rate with the temperature of the critical/sonic point which mainly reflects the different radii and resulting gravitational accelerations. Moreover, we obtain a relation between the observed effective temperature and the transformed mass-loss rate which seems to be largely independent of the underlying stellar parameters. The relation shifts for different clumping factors in the outer wind. Below a characteristic value of -4.5, the slope of this relation changes and the winds become transparent for He II ionizing photons.
CONCLUSIONS: The mass loss of cWR stars is a high-dimensional problem but also shows inherent scalings which can be used to obtain an approximation of the observed effective temperature. (…)

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A. Sander, R. Lefever, L. Poniatowski, et. al.
Fri, 6 Jan 23
22/55

Comments: 16 pages + 5 page appendix, 17+9 figures, 3+2 tables. Accepted for publication in A&A

Investigating the morphology and CO gas kinematics of Sh2-112 region [GA]

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http://arxiv.org/abs/2301.02048


We present a study of the molecular cloud in Sh2-112 massive star forming region using the 3-2 transition of CO isotopologues – CO, 13CO, and C18O; supplemented in part by CGPS HI line emission and MSX data. Sh2-112 is an optically visible region powered by an O8V type massive star BD +45 3216, and hosts two Red MSX Survey sources – G083.7962+03.3058 and G083.7071+03.2817 – classified as HII region and young stellar object, respectively. Reduced spectral data products from the James Clerk Maxwell Telescope archive, centered on the two RMS objects with ~7’x7′ field of view each, were utilised for the purpose. The 13CO(3-2) channel map of the region shows the molecular cloud to have filamentary extensions directed away from the massive star, which also seems to be at the edge of a cavity like structure. Multiple molecular cloud protrusions into this cavity structure host local peaks of emission. The integrated emission map of the region constructed from only those emission clumps detected above 5$\sigma$ level in the position-position-velocity space affirms the same. MSX sources were found distributed along the cavity boundary where the gas has the been compressed. Spectral extraction at these positions yielded high Mach numbers and low ratios of thermal to non-thermal pressure, suggesting a dominance of supersonic and non-thermal motion in the cloud.

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K. Mallick, S. Sharma, L. Dewangan, et. al.
Fri, 6 Jan 23
26/55

Comments: 15 Pages, 11 Figures, Accepted in Journal of Astrophysics and Astronomy (JAA)

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -XIII. Ongoing triggered star formation within clump-fed scenario found in the massive ($\sim1500$ $\rm M_\odot$) clump [GA]

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http://arxiv.org/abs/2301.01937


Whether ionization feedback triggers the formation of massive stars is highly debated. Using ALMA 3 mm observations with a spatial resolution of $\sim 0.05$ pc and a mass sensitivity of 1.1 $\rm M_\odot$ beam$^{-1}$ at 20 K, we investigate the star formation and gas flow structures within the ionizing feedback-driven structure, a clump-scale massive ($\gtrsim 1500$ $\rm M_\odot$) bright-rimmed cloud (BRC) associated with IRAS 18290-0924. This BRC is bound only if external compression from ionized gas is considered. A small-scale ($\lesssim1$ pc) age sequence along the direction of ionizing radiation is revealed for the embedded cores and protostars, which suggests triggered star formation via radiation-driven implosion (RDI). Furthermore, filamentary gas structures converge towards the cores located in the BRC’s center, indicating that these filaments are fueling mass towards cores. The local core-scale mass infall rate derived from H$^{13}$CO$^+$ $J=1-0$ blue profile is of the same order of magnitude as the filamentary mass inflow rate, approximately 1 $\rm M_\odot$ kyr$^{-1}$. A photodissociation region (PDR) covering the irradiated clump surface is detected in several molecules, such as CCH, HCO$^+$, and CS whereas the spatial distribution stratification of these molecules is indistinct. CCH spectra of the PDR possibly indicate a photoevaporation flow leaving the clump surface with a projected velocity of $\sim2$ km s$^{-1}$. Our new observations show that RDI accompanied by a clump-fed process is operating in this massive BRC. Whether this combined process works in other massive BRCs is worth exploring with dedicated surveys.

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S. Zhang, K. Wang, T. Liu, et. al.
Fri, 6 Jan 23
30/55

Comments: 34 pages with 20 figures, Accepted by MNRAS on 2022 December 28

Discovery of a resolved white dwarf-brown dwarf binary with a small projected separation: SDSS J222551.65+001637.7AB [SSA]

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http://arxiv.org/abs/2301.02101


We present the confirmation of SDSS J222551.65+001637.7AB as a closely separated, resolved, white dwarf-brown dwarf binary. We have obtained spectroscopy from GNIRS and seeing-limited $K_s$-band imaging from NIRI on Gemini North. The target is spatially resolved into its constituent components: a 10926$ \pm$ 246 K white dwarf, with log $g = 8.214 \pm 0.168$ and a mass of 0.66$^{+0.11}{-0.06}$ M${\odot}$, and an L4 brown dwarf companion, which are separated by $0.9498 \pm 0.0022$”. We derive the fundamental properties of the companion from the Sonora-Bobcat evolutionary models, finding a mass of $25-53$ M${\text{Jup}}$ and a radius of $0.101-0.128$ R${\odot}$ for the brown dwarf, at a confidence level of 1$\sigma$. We use wdwarfdate to determine the age of the binary as $1.97^{+4.41}{-0.76}$ Gyr. A kinematic analysis shows that this binary is likely a member of the thick disc. The distance to the binary is 218$^{+14}{-13}$ pc, and hence the projected separation of the binary is 207$^{+13}_{-12}$ AU. Whilst the white dwarf progenitor was on the main sequence the binary separation would have been $69 \pm 5$ AU. SDSS J222551.65+001637.7AB is the third closest spatially resolved white dwarf-brown dwarf binary after GD 165AB and PHL 5038AB.

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J. French, S. Casewell, T. Dupuy, et. al.
Fri, 6 Jan 23
37/55

Comments: 9 pages, 6 figures. Accepted for publication in MNRAS

Fragmentation of the High-mass "Starless'' Core G10.21-0.31: a Coherent Evolutionary Picture for Star Formation [GA]

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http://arxiv.org/abs/2301.02070


G10.21-0.31 is a 70 $\mu$m-dark high-mass starless core ($M>300$ $\mathrm{M_{\odot}}$ within $r<0.15$ pc) identified in $Spitzer$, $Herschel$, and APEX continuum surveys, and is believed to harbor the initial stages of high-mass star formation. We present ALMA and SMA observations to resolve the internal structure of this promising high-mass starless core. Sensitive high-resolution ALMA 1.3 mm dust continuum emission reveals three cores of mass ranging 11-18 $\mathrm{M_{\odot}}$, characterized by a turbulent fragmentation. Core 1, 2, and 3 represent a coherent evolution at three different evolutionary stages, characterized by outflows (CO, SiO), gas temperature ($\mathrm{H_2CO}$), and deuteration ($\mathrm{N_2D^+/N_2H^+}$). We confirm the potential to form high-mass stars in G10.21 and explore the evolution path of high-mass star formation. Yet, no high-mass prestellar core is present in G10.21. This suggests a dynamical star formation where cores grow in mass over time.

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W. Jiao, K. Wang, T. Pillai, et. al.
Fri, 6 Jan 23
40/55

Comments: 30 pages, 13 figures; accepted for publication in ApJ

Multi-stage reconnection powering a solar coronal jet [SSA]

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http://arxiv.org/abs/2301.02034


Coronal jets are short-lived eruptive features commonly observed in polar coronal holes and are thought to play a key role in the transfer of mass and energy into the solar corona. We describe unique contemporaneous observations of a coronal blowout jet seen by the Extreme Ultraviolet Imager onboard the Solar Orbiter spacecraft (SO/EUI) and the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory (SDO/AIA). The coronal jet erupted from the south polar coronal hole, and was observed with high spatial and temporal resolution by both instruments. This enabled identification of the different stages of a breakout reconnection process producing the observed jet. We find bulk plasma flow kinematics of ~100-200 km/s across the lifetime of its observed propagation, with a distinct kink in the jet where it impacted and was subsequently guided by a nearby polar plume. We also identify a faint faster feature ahead of the bulk plasma motion propagating with a velocity of ~715 km/s which we attribute to untwisting of newly reconnected field lines during the eruption. A Differential Emission Measure (DEM) analysis using the SDO/AIA observations revealed a very weak jet signal, indicating that the erupting material was likely much cooler than the coronal passbands used to derive the DEM. This is consistent with the very bright appearance of the jet in the Lyman-$\alpha$ passband observed by SO/EUI. The DEM was used to estimate the radiative thermal energy of the source region of the coronal jet, finding a value of $\sim2\times10^{24}$ ergs, comparable to the energy of a nanoflare.

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D. Long, L. Chitta, D. Baker, et. al.
Fri, 6 Jan 23
43/55

Comments: 12 pages, 6 figures, accepted for publication in The Astrophysical Journal

Re-calibration of the Sunspot Number: Status Report [SSA]

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http://arxiv.org/abs/2301.02084


We report progress on the ongoing recalibration of the Wolf sunspot number (SN) and Group sunspot number (GN) following the release of version 2.0 of SN in 2015. This report constitutes both an update of the efforts reported in the 2016 Topical Issue of Solar Physics and a summary of work by the International Space Science Institute (ISSI) International Team formed in 2017 to develop optimal SN and GN re-construction methods while continuing to expand the historical sunspot number database. Significant progress has been made on the database side while more work is needed to bring the various proposed SN and (primarily) GN reconstruction methods closer to maturity, after which the new reconstructions (or combinations thereof) can be compared with (a) “benchmark” expectations for any normalization scheme (e.g., a general increase in observer normalization factors going back in time), and (b) independent proxy data series such as F10.7 and the daily range of variations of Earth’s undisturbed magnetic field. New versions of the underlying databases for SN and GN will shortly become available for years through 2022 and we anticipate the release of next versions of these two time series in 2024.

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F. Clette, L. Lefèvre, T. Chatzistergos, et. al.
Fri, 6 Jan 23
48/55

Comments: 21 figures, 4 tables. To be published in Solar Physics

The Co-Ordinated Radio and Infrared Survey for High-Mass Star Formation. V. The CORNISH-South Survey and Catalogue [GA]

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http://arxiv.org/abs/2301.01988


We present the first high spatial resolution radio continuum survey of the southern Galactic plane. The CORNISH project has mapped the region defined by $295^{\circ} < l < 350^{\circ}$; $|b| < 1^{\circ}$ at 5.5-GHz, with a resolution of 2.5$^{”}$ (FWHM). As with the CORNISH-North survey, this is designed to primarily provide matching radio data to the Spitzer GLIMPSE survey region. The CORNISH-South survey achieved a root mean square noise level of $\sim$ 0.11 mJy beam$^{-1}$, using the 6A configuration of the Australia Telescope Compact Array (ATCA). In this paper, we discuss the observations, data processing and measurements of the source properties. Above a 7$\sigma$ detection limit, 4701 sources were detected, and their ensemble properties show similar distributions with their northern counterparts. The catalogue is highly reliable and is complete to 90 per cent at a flux density level of 1.1 mJy. We developed a new way of measuring the integrated flux densities and angular sizes of non-Gaussian sources. The catalogue primarily provides positions, flux density measurements and angular sizes. All sources with IR counterparts at 8$\mu m$ have been visually classified, utilizing additional imaging data from optical, near-IR, mid-IR, far-IR and sub-millimetre galactic plane surveys. This has resulted in the detection of 524 H II regions of which 255 are ultra-compact H II regions, 287 planetary nebulae, 79 radio stars and 6 massive young stellar objects. The rest of the sources are likely to be extra-galactic. These data are particularly important in the characterization and population studies of compact ionized sources such as UCHII regions and PNe towards the Galactic mid-plane.

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T. Irabor, M. Hoare, M. Burton, et. al.
Fri, 6 Jan 23
49/55

Comments: N/A

UOCS-IX. AstroSat/UVIT study of the open cluster NGC 2818: Blue Stragglers, Yellow Stragglers, Planetary Nebula, and their membership [SSA]

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http://arxiv.org/abs/2301.01943


We present the first far-UV (FUV) imaging results of the intermediate-age Galactic open cluster NGC 2818 that has a Planetary nebula (PN) within the field using images taken from the Ultra-violet Imaging Telescope (UVIT) aboard AstroSat. We identify cluster members by combining UVIT-detected sources with Gaia EDR3 data. We detect four bright and hot blue straggler stars (BSSs) and two yellow straggler stars (YSSs) based on their location in the optical and FUV-optical color-magnitude diagrams. Based on the parameters estimated using Spectral Energy Distribution (SED), we infer that BSSs are either collisional products or might have undetectable white dwarf (WD) companions. Our photometric analysis of YSSs confirms their binarity, consistent with the spectroscopic results. We find YSSs to be formed through a mass-transfer scenario and the hot components are likely to be A-type subdwarfs. A comparison of the radial velocity (RV), Gaia EDR3 proper motion of the PN with the cluster, and reddening towards the PN and the cluster does not rule out the membership of the PN. Comparing the central star’s position with theoretical pAGB models suggest that it has already entered the WD cooling phase, and its mass is deduced to be ~0.66Msun. The corresponding progenitor mass turns out to be ~2.1Msun, comparable to the turn-off mass of the cluster, implying that the progenitor could have formed in the cluster. We suggest that the NGC 2818 might be one of the few known clusters to host a PN, providing a unique opportunity to test stellar evolution models.

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S. Rani, G. Pandey, A. Subramaniam, et. al.
Fri, 6 Jan 23
51/55

Comments: 20 pages, 12 figures, 4 tables, Accepted for publication in ApJ

Inferring the impact of feedback on the matter distribution using the Sunyaev Zel'dovich effect: Insights from CAMELS simulations and ACT+DES data [CEA]

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http://arxiv.org/abs/2301.02186


Feedback from active galactic nuclei and stellar processes changes the matter distribution on small scales, leading to significant systematic uncertainty in weak lensing constraints on cosmology. We investigate how the observable properties of group-scale halos can constrain feedback’s impact on the matter distribution using Cosmology and Astrophysics with MachinE Learning Simulations (CAMELS). Extending the results of previous work to smaller halo masses and higher wavenumber, $k$, we find that the baryon fraction in halos contains significant information about the impact of feedback on the matter power spectrum. We explore how the thermal Sunyaev Zel’dovich (tSZ) signal from group-scale halos contains similar information. Using recent Dark Energy Survey (DES) weak lensing and Atacama Cosmology Telescope (ACT) tSZ cross-correlation measurements and models trained on CAMELS, we obtain $10\%$ constraints on feedback effects on the power spectrum at $k \sim 5\, h/{\rm Mpc}$. We show that with future surveys, it will be possible to constrain baryonic effects on the power spectrum to $\mathcal{O}(<1\%)$ at $k = 1\, h/{\rm Mpc}$ and $\mathcal{O}(3\%)$ at $k = 5\, h/{\rm Mpc}$ using the methods that we introduce here. Finally, we investigate the impact of feedback on the matter bispectrum, finding that tSZ observables are highly informative in this case.

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S. Pandey, K. Lehman, E. Baxter, et. al.
Fri, 6 Jan 23
53/55

Comments: 18 pages, 15 figures. Comments are welcome

Effect of stellar rotation on the development of post-shock instabilities during core-collapse supernovae [HEAP]

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http://arxiv.org/abs/2301.01962


The growth of instabilities is key to trigger a supernova explosion during the phase of stalled shock, immediately after the birth of a proto-neutron star (PNS). We assess the effect of stellar rotation on neutrino-driven convection and SASI when neutrino heating is taken into account. Rotation affects the frequency of the mode m=2 detectable with gravitational waves (GW). We use a linear stability analysis in the equatorial plane between the PNS and the stationary shock and consider a large range of specific angular momenta, neutrino luminosities and mass accretion rates. The nature of the dominant instability depends on the convection parameter chi and the rotation rate. Convective modes with chi>=5 are hampered by differential rotation. At smaller chi, however, mixed SASI-convective modes with a large angular scale m=1,2,3 benefit from rotation and become dominant for relatively low rotation rates at which centrifugal effects are small. For rotation rates >0.3 Keplerian rotation at the PNS surface (KPNS), the growth rate of the dominant mode depends weakly on neutrino heating which highlights a new instability regime. Its frequency is surprisingly independent of the heating rate, with a strong prograde spiral m=2 dominating over a large parameter range, favourable to the production of GW. A simple linear relation exists between the dominant oscillation frequency and the specific angular momentum. Three regimes are distinguished. For rotation rates <0.1KPNS, differential rotation has a quadratic effect on equatorial purely convective modes and a linear destabilizing effect on SASI. Intermediate rotation rates (0.1 to 0.3KPNS) lead to the emergence of mixed SASI/convection/rotation modes involving large angular scales. Finally, strong rotation erases the influence of buoyancy on the instability. This allows for a reduction of the parameter space, which is valuable for GW analysis.

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A. Buellet, T. Foglizzo, J. Guilet, et. al.
Fri, 6 Jan 23
54/55

Comments: 16 pages, 17 figures, submitted to A&A

The height of convective plumes in the red supergiant $μ$ Cep [SSA]

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http://arxiv.org/abs/2301.01326


Aims. We seek to understand convection in red supergiants and the mechanisms that trigger the mass loss from cool evolved stars. Methods. Linear spectropolarimetry of the atomic lines of the spectrum of $\mu$ Cep reveals information well outside the wavelength range expected from previous models. This is interpreted as structures in expansion that are visible in the front hemisphere and sometimes also in the back hemisphere. We model the plasma distribution together with its associated velocities through an inversion algorithm to fit the observed linear polarization. Results. We find that supposing the existence of plasma beyond the limb rising high enough to be visible above it can explain the observed linear polarization signatures as well as their evolution in time. From this we are able to infer the geometric heights of the convective plumes and establish that this hot plasma rises to at least 1.1 R*. Conclusions. $\mu$ Cep appears to be in an active phase in which plasma rises often above 1.1 R* . We generalize this result to all red supergiants in a similarly evolved stage, which at certain epochs may easily send plasma to greater heights, as $\mu$ Cep appears to be doing at present. Plasma rising to such heights can easily escape the stellar gravity.

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A. Ariste, M. Wavasseur, P. Mathias, et. al.
Thu, 5 Jan 23
1/51

Comments: Accepted for publication in A&A

Delayed Development of Cool Plasmas in X-ray Flares from kappa1 Ceti [HEAP]

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http://arxiv.org/abs/2301.01377


The Neutron star Interior Composition ExploreR (NICER) X-ray observatory observed two powerful X-ray flares equivalent to superflares from the nearby young solar-like star, kappa1 Ceti, in 2019. NICER follows each flare from the onset through the early decay, collecting over 30 cts s-1 near the peak, enabling a detailed spectral variation study of the flare rise. The flare in September varies quickly in ~800 sec, while the flare in December has a few times longer timescale. In both flares, the hard band (2-4 keV) light curves show typical stellar X-ray flare variations with a rapid rise and slow decay, while the soft X-ray light curves, especially of the September flare, have prolonged flat peaks. The time-resolved spectra require two temperature plasma components at kT ~0.3-1 keV and ~2-4 keV. Both components vary similarly, but the cool component lags by ~200 sec with a 4-6 times smaller emission measure (EM) compared to the hot component. A comparison with hydrodynamic flare loop simulations indicates that the cool component originates from X-ray plasma near the magnetic loop footpoints, which mainly cools via thermal conduction. The time lag represents the travel time of the evaporated gas through the entire flare loop. The cool component has several times smaller EM than its simulated counterpart, suggesting a suppression of conductive cooling possibly by the expansion of the loop cross-sectional area or turbulent fluctuations. The cool component’s time lag and small EM ratio provide important constraints on the flare loop geometry.

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K. Hamaguchi, J. Reep, V. Airapetian, et. al.
Thu, 5 Jan 23
2/51

Comments: 21 pages, 12 figures, to be published in the Astrophysical Journal

Binary black hole spins: model selection with GWTC-3 [HEAP]

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http://arxiv.org/abs/2301.01312


The origin of the spins of stellar-mass black holes is still controversial, and angular momentum transport inside massive stars is one of the main sources of uncertainty. Here, we apply hierarchical Bayesian inference to derive constraints on spin models from the 59 most confident binary black hole merger events in the third gravitational-wave transient catalogue (GWTC-3). We consider up to five parameters: chirp mass, mass ratio, redshift, effective spin, and precessing spin. For model selection, we use a set of binary population synthesis simulations spanning drastically different assumptions for black hole spins and natal kicks. In particular, our spin models range from maximal to minimal efficiency of angular momentum transport in stars. We find that, if we include the precessing spin parameter into our analysis, models predicting only vanishingly small spins are in tension with GWTC-3 data. On the other hand, models in which most spins are vanishingly small, but that also include a sub-population of tidally spun-up black holes are a good match to the data. Our results show that the precessing spin parameter has a crucial impact on model selection.

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P. Carole, M. Michela, S. Filippo, et. al.
Thu, 5 Jan 23
6/51

Comments: 11 pages, submitted to mnras. arXiv admin note: text overlap with arXiv:2102.12495 by other authors

Lyman-alpha Scattering Models Trace Accretion and Outflow Kinematics in T Tauri Systems [SSA]

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http://arxiv.org/abs/2301.01761


T Tauri stars produce broad Lyman-alpha emission lines that contribute $\sim$88% of the total UV flux incident on the inner circumstellar disks. Lyman-alpha photons are generated at the accretion shocks and in the protostellar chromospheres and must travel through accretion flows, winds and jets, the protoplanetary disks, and the interstellar medium before reaching the observer. This trajectory produces asymmetric, double-peaked features that carry kinematic and opacity signatures of the disk environments. To understand the link between the evolution of Lyman-alpha emission lines and the disks themselves, we model HST-COS spectra from targets included in Data Release 3 of the Hubble UV Legacy Library of Young Stars as Essential Standards (ULLYSES) program. We find that resonant scattering in a simple spherical expanding shell is able to reproduce the high velocity emission line wings, providing estimates of the average velocities within the bulk intervening H I. The model velocities are significantly correlated with the K band veiling, indicating a turnover from Lyman-alpha profiles absorbed by outflowing winds to emission lines suppressed by accretion flows as the hot inner disk is depleted. Just 30% of targets in our sample have profiles with red-shifted absorption from accretion flows, many of which have resolved dust gaps. At this stage, Lyman-alpha photons may no longer intersect with disk winds along the path to the observer. Our results point to a significant evolution of Lyman-alpha irradiation within the gas disks over time, which may lead to chemical differences that are observable with ALMA and JWST.

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N. Arulanantham, M. Gronke, E. Fiorellino, et. al.
Thu, 5 Jan 23
7/51

Comments: accepted to ApJ

The intense production of silicates during the final AGB phases of intermediate mass stars [SSA]

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http://arxiv.org/abs/2301.01647


The formation of silicates in circumstellar envelopes of stars evolving through the AGB is still debated given the uncertainties affecting stellar evolution modelling, the description of the dust formation process, and the capability of silicate grains to accelerate stellar outflows via radiation pressure. We study the formation of dust in the winds of intermediate mass (M $\geq 4 M_{\odot}$) stars of solar metallicity while evolving through the AGB phase. We tested the different treatments of the mass-loss mechanism by this class of stars, with the aim of assessing their contribution to the general enrichment of silicates of the interstellar medium of galaxies. We consider a sub-sample of AGB stars, whose SED is characterised by deep absorption features at $10$ and $18\mu$m, which can be regarded as the class of stars providing the most relevant contribution to the silicates’ production across the Universe. Results from stellar evolution and dust formation modelling were used to fit the observed SED and to reproduce, at the same time, the detected pulsation periods and the derived surface chemical composition. This analysis leads to the derivation of tight constraints on the silicates’ production rates experienced by these sources during the final AGB stages. Two out of the four sources investigated are interpreted as stars currently undergoing HBB, evolving through phases close to the stage when the mass-loss rate is largest. The remaining two stars are likely evolving through the very final AGB phases, after HBB was turned off by the gradual consumption of the convective mantle. Mass-loss rates of the order of $1-2\times 10^{-4} M_{\odot}/$yr are required when looking for consistency with the observational evidence. These results indicate the need for a revision of the silicate yields by intermediate mass stars, which are found to be $\sim 3$ times higher than previously determined.

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E. Marini, F. Dell’Agli, D. Kamath, et. al.
Thu, 5 Jan 23
9/51

Comments: N/A

Reaching the boundary between stellar kinematic groups and very wide binaries. IV. The widest Washington double star systems with rho > 1000 arcsec in Gaia DR3 [SSA]

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http://arxiv.org/abs/2301.01722


Aims: With the latest Gaia DR3 data, we analyse the widest pairs in the Washington Double Star (WDS) catalogue with angular separations, $\rho$, greater than 1000 arcsec. Methods: We confirmed the pair’s membership to stellar systems based on common proper motions, parallaxes, and (when available) radial velocities, together with the locii of the individual components in colour-magnitude diagrams. We also looked for additional closer companions to the ultrawide pairs, either reported by WDS or found by us with a new Gaia astrometric search. In addition, we determined masses for each star (and white dwarf) and, with the projected physical separation, computed the gravitational potential energy, |Ug*|, of the systems. Results: Of the 155159 pairs currently catalogued by WDS, there are 504 with $\rho$ > 1000 arcsec. Of these, only 2 ultrawide pairs have not been identified, 10 do not have any available astrometry, 339 have not passed a conservative filtering in proper motion or parallax, 59 are members of young stellar kinematic groups, associations or open clusters, and only 94 remain as bona fide ultrawide pairs in the galactic field. Accounting for the additional members at shorter separations identified in a complementary astrometric and bibliographic search, we found 79 new stars (39 reported, plus 40 not reported by WDS) in 94 ultrawide stellar systems. This sample is expanded when including new close binary candidates with large Gaia DR3 RUWE, $\sigma_{Vr}$, or a proper motion anomaly. Furthermore, the large fraction of subsystems and the non-hierarchical configurations of many wide systems with three or more stars is remarkable.

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J. González-Payo, J. Caballero and M. Cortés-Contreras
Thu, 5 Jan 23
10/51

Comments: Accepted to A&A. 38 Pages, 8 figures and 9 tables (4 tables online)

Formation Of The Lyman Continuum During Solar Flares [SSA]

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http://arxiv.org/abs/2301.01648


The Lyman Continuum (LyC; $<911.12$\AA) forms at the top of the chromosphere in the quiet-Sun, making LyC a powerful tool for probing the chromospheric plasma during solar flares. To understand the effects of non-thermal energy deposition in the chromosphere during flares, we analysed LyC profiles from a grid of field-aligned radiative hydrodynamic models generated using the RADYN code as part of the F-CHROMA project. The spectral response of LyC, the temporal evolution of the departure coefficient of hydrogen, $b_1$, and the color temperature, $T_c$, in response to a range of non-thermal electron distribution functions, were investigated. The LyC intensity was seen to increase by 4-5.5 orders of magnitude during solar flares, responding most strongly to the non-thermal electron flux of the beam. Generally, $b_1$ decreased from $10^2$-$10^3$ to closer to unity during solar flares, indicating a stronger coupling to local conditions, while $T_c$ increased from $8$-$9$kK to $10$-$16$kK. $T_c$ was found to be approximately equal to the electron temperature of the plasma when $b_1$ was at a minimum. Both optically thick and optically thin components of LyC were found in agreement with the interpretation of recent observations. The optically thick layer forms deeper in the chromosphere during a flare compared to quiescent periods, whereas the optically thin layers form at higher altitudes due to chromospheric evaporation, in low-temperature, high-density regions propagating upwards. We put these results in the context of current and future missions.

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S. McLaughlin, R. Milligan, G. Kerr, et. al.
Thu, 5 Jan 23
20/51

Comments: Accepted for publication in The Astrophysical Journal: 18 pages, 16 Figures

Solar Sail Propulsion by 2050: An Enabling Capability for Heliophysics Missions [IMA]

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http://arxiv.org/abs/2301.01297


Solar sails enable missions to observe the solar environment from unique vantage points, such as sustained observations away from the Sun-Earth line; sub-L1 station keeping; high inclination solar orbits; Earth polar-sitting and polar-viewing observatories; fast transit missions to study heliosphere to interstellar medium transition, as well as missions of interest across a broad user community. Recent and planned demonstration missions make this technology ready for use on near-term science missions.

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L. Johnson, N. Barnes, M. Ceriotti, et. al.
Thu, 5 Jan 23
24/51

Comments: Heliophysics 2050 White Paper

Origin of Quasi-Periodic Pulsation at the Base of Kink Unstable Jet [SSA]

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http://arxiv.org/abs/2301.01534


We study a blowout jet that occurs at the west limb of the Sun on August 29$^{th}$, 2014 using high-resolution imaging/spectroscopic observations provided by SDO/AIA and IRIS. An inverse $\gamma$-shape flux-rope appears before the jet{–} morphological indication of the onset of kink instability. The twisted field lines of kink-unstable flux-rope reconnect at its bright knot and launch the blowout jet at $\approx$06:30:43 UT with an average speed of 234 km s$^{-1}$. Just after the launch, the northern leg of the flux rope erupts completely. The time-distance diagrams show multiple spikes or bright dots, which is the result of periodic fluctuations, i.e., quasi-periodic fluctuations (QPPs). The wavelet analysis confirms that QPPs have a dominant period of $\approx$ 03 minutes. IRIS spectra (Si~{\sc iv}, C~{\sc ii}, and Mg~{\sc ii}) may also indicate the occurrence of magnetic reconnection through existence of broad $\&$ complex profiles and bi-directional flows in the jet. Further, we have found that line broadening is periodic with a period of $\approx$ 03 minutes, and plasma upflow is always occurs when the line width is high, i.e., multiple reconnection may produce periodic line broadening. The EM curves also show the same period of $\approx$ 03 minutes in different temperature bins. The images and EM show that this jets spire is mainly cool (chromospheric/transition region) rather than hot (coronal) material. Further, line broadening, intensity, and EM curves have a period of $\approx$03 minutes, which strongly supports that multiple magnetic reconnection triggers QPPs in the blowout jet.

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S. Mishra, K. Sangal, P. Kayshap, et. al.
Thu, 5 Jan 23
27/51

Comments: The Astrophysical Journal (In press), 25 pages, 12 figures

Identifying preflare spectral features using explainable artificial intelligence [SSA]

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http://arxiv.org/abs/2301.01560


The prediction of solar flares is of practical and scientific interest; however, many machine learning methods used for this prediction task do not provide the physical explanations behind a model’s performance. We made use of two recently developed explainable artificial intelligence techniques called gradient-weighted class activation mapping (Grad-CAM) and expected gradients (EG) to reveal the decision-making process behind a high-performance neural network that has been trained to distinguish between MgII spectra derived from flaring and nonflaring active regions, a fact that can be applied to the task of short timescale flare forecasting. The two techniques generate visual explanations (heatmaps) that can be projected back onto the spectra, allowing for the identification of features that are strongly associated with precursory flare activity. We automated the search for explainable interpretations on the level of individual wavelengths, and provide multiple examples of flare prediction using IRIS spectral data, finding that prediction scores in general increase before flare onset. Large IRIS rasters that cover a significant portion of the active region and coincide with small preflare brightenings both in IRIS and SDO/AIA images tend to lead to better forecasts. The models reveal that MgII triplet emission, flows, as well as broad and highly asymmetric spectra are all important for the task of flare prediction. Additionally, we find that intensity is only weakly correlated to a spectrum’s prediction score, meaning that low intensity spectra can still be of great importance for the flare prediction task, and that $78$% of the time, the position of the model’s maximum attention along the slit during the preflare phase is predictive of the location of the flare’s maximum UV emission

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B. Panos, L. Kleint and J. Zbinden
Thu, 5 Jan 23
31/51

Comments: N/A

Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS): Characterization of the young star T CrA and its circumstellar environment [SSA]

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http://arxiv.org/abs/2301.01486


Birth environments of young stars have strong imprints on the star itself and their surroundings. We present a detailed analysis of the wealthy circumstellar environment around the young Herbig Ae/Be star TCrA. Our aim is to understand the nature of the stellar system and the extended circumstellar structures as seen in scattered light images. We conduct our analysis combining archival data, and new adaptive optics high-contrast and high-resolution images. The scattered light images reveal the presence of a complex environment composed of a bright forward scattering rim of the disk’s surface that is seen at very high inclination, a dark lane of the disk midplane, bipolar outflows, and streamer features likely tracing infalling material from the surrounding birth cloud onto the disk. The analysis of the light curve suggests the star is a binary with a period of 29.6yrs. The comparison of the scattered light images with ALMA continuum and 12CO line emission shows the disk is in keplerian rotation, with the northern side of the outflowing material receding, while the southern side approaching the observer. The disk is itself seen edge-on. The direction of the outflows seen in scattered light is in agreement with the direction of the more distant molecular hydrogen emission-line objects (MHOs) associated to the star. Modeling of the SED using a radiative transfer scheme well agrees with the proposed configuration, as well as the hydrodynamical simulation performed using a Smoothed Particle Hydrodynamics code. We find evidence of streamers of accreting material around TCrA. These streamers connect the filament along which TCrA is forming with the outer parts of the disk, suggesting that the strong misalignment between the inner and outer disk is due to a change in the direction of the angular momentum of the material accreting on the disk during the late phase of star formation.

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E. Rigliaco, R. Gratton, S. Ceppi, et. al.
Thu, 5 Jan 23
38/51

Comments: 17 pages, 14 figures

Strong magnetic fields detected in the cores of 11 red giant stars using gravity-mode period spacings [SSA]

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http://arxiv.org/abs/2301.01308


Despite their importance in stellar evolution, little is known about magnetic fields in the interior of stars. The recent seismic detection of magnetic fields in the core of several red giant stars has given measurements of their strength and information on their topology. We revisit the puzzling case of hydrogen-shell burning giants that show deviations from the expected regular period spacing of gravity modes. These stars also tend to have a too low measured period spacing compared to their counterparts. We here show that these two features are well accounted for by strong magnetic fields in the cores of these stars. For 11 Kepler red giants showing these anomalies, we place lower limits on the core field strengths ranging from 40 to 610 kG. For one star, the measured field exceeds the critical field above which gravity waves no longer propagate in the core. We find that this star shows mixed mode suppression at low frequency, which further suggests that this phenomenon might be related to strong core magnetic fields.

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S. Deheuvels, G. Li, J. Ballot, et. al.
Thu, 5 Jan 23
40/51

Comments: 10 pages, 7 figures, accepted as an Letter in A&A

Fast methods to track grain coagulation and ionization. III. Protostellar collapse with non-ideal MHD [SSA]

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http://arxiv.org/abs/2301.01510


Dust grains influence many aspects of star formation, including planet formation, opacities for radiative transfer, chemistry, and the magnetic field via Ohmic, Hall, and ambipolar diffusion. The size distribution of the dust grains is the primary characteristic influencing all these aspects. Grain size increases by coagulation throughout the star formation process. We describe here numerical simulations of protostellar collapse using methods described in earlier papers of this series. We compute the evolution of the grain size distribution from coagulation and the non-ideal magnetohydrodynamics effects self-consistently and at low numerical cost. We find that the coagulation efficiency is mostly affected by the time spent in high-density regions. Starting from sub-micron radii, grain sizes reach more than 100 {\mu}m in an inner protoplanetary disk that is only 1000 years old. We also show that the growth of grains significantly affects the resistivities, and indirectly the dynamics and angular momentum of the disk.

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P. Marchand, U. Lebreuilly, M. Low, et. al.
Thu, 5 Jan 23
41/51

Comments: 11 pages, 9 figures, accepted in A&A

Detection of the longest periodic variability in 6.7 GHz methanol masers of G5.900-0.430 [SSA]

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http://arxiv.org/abs/2301.01432


Long term monitoring observations with the Hitachi 32-m radio telescope of the 6.7 GHz methanol masers associated with the high mass star-forming region G5.900-0.430 is presented. A period of flux variability at approximately 1260 days, is detected in the features at VLSR = 9.77 and 10.84 km/s while a secondary shorter period, 130.6 days, is determined for the 0.66 km/s feature. This is only the second source which has two different periods. The period of ~1260 days is approximately twice as long as the longest known period of 6.7 GHz methanol masers. The variability pattern of the symmetric sine curves and the consistency with the expected period-luminosity relation suggest that the mechanism of maser flux variability of 9.77 and 10.84 km/s features in this source can be explained by protostellar pulsation instability. On the other hand, because the 0.66 km/s feature has an intermittent and asymmetric variability profile, we propose this feature is explained by the CWB or spiral shock models. Obtaining the spatial distribution of the 0.66 km/s feature using an VLBI will lead to a better understanding of this source.

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Y. Tanabe, Y. Yonekura and M. Gordon
Thu, 5 Jan 23
50/51

Comments: N/A

Sub-Jovian desert of exoplanets at its boundaries: Parameter dependence along the main sequence [EPA]

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http://arxiv.org/abs/2301.01065


Context. The lack of sub-Jovian planets on orbits of $P_{\rm orb} < 3$ days is a puzzling aspect of galaxy formation with regard to the distribution of exoplanets whose origins are currently unresolved. Aims. The possible explanations behind the formation of the sub-Jovian or Neptunian desert include several scenarios that can lead to different shapes for the boundary, predicting various dependencies between the position of the boundary and the stellar parameters. Methods. We explored the exoplanet distribution in various 2D and 3D projections, revealing the stellar-dependent substructures in the $P_{\rm orb}-M_{P}$ and the $P_{\rm orb}-R_{P}$ parameter plane. Results. We demonstrate that the upper boundary includes a range of planets, namely, inflated hot Jupiters and normal hot Jupiters, in the two parameter planes, respectively. We confirm the dependence of the boundary on several stellar parameters and, based on a fuzzy clustering analysis, we provide quantitative formulae for the dependencies in groups of smaller and larger planets. The overall period-radius distribution shows chemical substructures as well, with the boundary being dependent on volatiles and alpha-elements, alongside marginal (to none) dependence found for refractory elements. Conclusions. These findings confirm multiple plausible causes for the formation of the desert, particularly preferring those scenarios related to the irradiation-driven loss of the atmospheres of moderately massive planets as the predominant process in shaping planetary distributions.

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G. M, S. Kálmán, L. Borsato, et. al.
Wed, 4 Jan 23
1/43

Comments: Accepted for publication in A&A; 11 pages, 11 figuress

From dark matter halos to pre-stellar cores: High resolution follow-up of cosmological Lyman-Werner simulations [GA]

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http://arxiv.org/abs/2301.00828


Molecular hydrogen allows cooling in primordial gas, facilitating its collapse into Population III stars within primordial halos. Lyman-Werner (LW) radiation from these stars can escape the halo and delay further star formation by destroying H$2$ in other halos. As cosmological simulations show that increasing the background LW field strength increases the average halo mass required for star formation, we perform follow-up simulations of selected halos to investigate the knock-on effects this has on the Population III IMF. We follow 5 halos for each of the $J{21}$ = 0, 0.01 and 0.1 LW field strengths, resolving the pre-stellar core density of $10^{-6}$ g cm$^{-3}$ (10$^{18}$ cm$^{-3}$) before inserting sink particles and following the fragmentation behaviour for hundreds of years further. We find that the mass accreted onto sinks by the end of the simulations is proportional to the mass within the $\sim 10^{-2}$ pc molecular core, which is not correlated to the initial mass of the halo. As such, the IMF shows little dependence on the LW strength. As the range of background LW field strengths tested here covers the most likely values from literature, we conclude that the IMF for so-called Pop III.2 stars is not significantly different from the initial population of Pop III.1 stars. The primordial IMF therefore likely remains unchanged until the formation of the next generation of Population II stars.

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L. Prole, A. Schauer, P. Clark, et. al.
Wed, 4 Jan 23
4/43

Comments: Submitted to MNRAS ID: MN-22-5075-MJ

Very low state in PY Per in 2022 [SSA]

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http://arxiv.org/abs/2301.00949


Using VSNET, VSOLJ, ASAS-SN and ATLAS observations, I found that the Z Cam star PY Per spent a long, faint low state reaching 19.1 mag at least between 2022 June and November. No dwarf nova outburst was recorded during this interval. TESS data during this low state showed two maxima in one orbital cycle and can be interpreted as an ellipsoidal modulation arising from the secondary. These observations suggest that the mass-transfer almost stopped during this low state and strengthen the identification of PY Per as a VY Scl star. PY Per had shown an unusual outburst resembling an SU UMa-type superoutburst less than half a year before (Kato 2022, arXiv:2204.12056) and these phenomena may have been physically related.

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T. Kato
Wed, 4 Jan 23
5/43

Comments: 6 pages, 3 figures, VSOLJ Variable Star Bulletin No. 104

Magnetic Reconnection as the Driver of the Solar Wind [SSA]

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http://arxiv.org/abs/2301.00903


We present EUV solar observations showing evidence for omnipresent jetting activity driven by small-scale magnetic reconnection at the base of the solar corona. We argue that the physical mechanism that heats and drives the solar wind at its source is ubiquitous magnetic reconnection in the form of small-scale jetting activity (i.e., a.k.a. jetlets). This jetting activity, like the solar wind and the heating of the coronal plasma, are ubiquitous regardless of the solar cycle phase. Each event arises from small-scale reconnection of opposite polarity magnetic fields producing a short-lived jet of hot plasma and Alfv\’en waves into the corona. The discrete nature of these jetlet events leads to intermittent outflows from the corona, which homogenize as they propagate away from the Sun and form the solar wind. This discovery establishes the importance of small-scale magnetic reconnection in solar and stellar atmospheres in understanding ubiquitous phenomena such as coronal heating and solar wind acceleration. Based on previous analyses linking the switchbacks to the magnetic network, we also argue that these new observations might provide the link between the magnetic activity at the base of the corona and the switchback solar wind phenomenon. These new observations need to be put in the bigger picture of the role of magnetic reconnection and the diverse form of jetting in the solar atmosphere.

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N. Raouafi, G. Stenborg, D. Seaton, et. al.
Wed, 4 Jan 23
15/43

Comments: 10 pages, 4 figures

Polar circumtriple planets and disks can only form close to a triple star [EPA]

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http://arxiv.org/abs/2301.01284


Observations of protoplanetary disks around binary and triple star systems suggest that misalignments between the orbital plane of the stars and the disks are common. Motivated by recent observations of polar circumbinary disks, we explore the possibility for polar circumtriple disks and therefore polar circumtriple planets that could form in such a disk. With n-body simulations and analytic methods we find that the inclusion of the third star, and the associated apsidal precession, significantly reduces the radial range of polar orbits so that circumtriple polar disks and planets can only be found close to the stellar system. Outside of a critical radius, that is typically in the range of 3-10 times the outer binary separation depending upon the binary parameters, the orbits behave the same as they do around a circular orbit binary. For some observed systems that have shorter period inner binaries, the critical radius is considerably larger. If polar circumtriple planets can form, we suggest that it is likely that they form in a disk that was subject to breaking.

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S. Lepp, R. Martin and S. Lubow
Wed, 4 Jan 23
16/43

Comments: Accepted for publication in ApJL

Science Platforms for Heliophysics Data Analysis [IMA]

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http://arxiv.org/abs/2301.00878


We recommend that NASA maintain and fund science platforms that enable interactive and scalable data analysis in order to maximize the scientific return of data collected from space-based instruments.

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M. Bobra, W. Barnes, T. Chen, et. al.
Wed, 4 Jan 23
17/43

Comments: Heliophysics 2050 White Paper

Updated characterization of long-period single companion by combining radial velocity, relative astrometry, and absolute astrometry [EPA]

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http://arxiv.org/abs/2301.01263


Context. Thanks to more than 20 years of monitoring, the radial velocity (RV) method has detected long-period companions (P > 10yr) around several dozens of stars. Yet, the true nature of these companions remains unclear because of the uncertainty as to the inclination of the companion orbital plane. Aims. We wish to constrain the orbital inclination and the true mass of long-period single companions. Methods. We used a Markov Chain Monte Carlo (MCMC) fitting algorithm to combine RV measurements with absolute astrometry and, when available, relative astrometry data. Results. We have lifted the sin(i) indetermination for 7 seven long-period companions. We find true masses in the planetary mass range for the candidate planets detected in the following systems: Epsilon Indi A, HD 13931, HD 115954, and HD 222155. The mass of HD 219077 b is close to the deuterium-burning limit and its nature is uncertain because of the imprecise mass of the host star. Using additional RV measurements, we refine the orbital parameters of HIP 70849 b and find a mass in the planetary range. By combining RV data with absolute and relative astrometry, we significantly improve the characterization of HD 211847 B and properly determine its mass, which appears to be in the low-mass star range. This work illustrates how Gaia and Hipparcos allow for the orbital properties and masses of long-period RV companions to be further constrained.

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F. Philipot, A. Lagrange, P. Rubini, et. al.
Wed, 4 Jan 23
21/43

Comments: 17 pages, 15 figures

Proton and electron temperatures in the solar wind and their correlations with the solar wind speed [SSA]

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http://arxiv.org/abs/2301.00852


The heating and acceleration of the solar wind remains one of the fundamental unsolved problems in heliophysics. It is usually observed that the proton temperature $T_i$ is highly correlated with the solar wind speed $V_{SW}$, while the electron temperature $T_e$ shows anti-correlation or no clear correlation with the solar wind speed. Here we inspect both Parker Solar Probe (PSP) and WIND data and compare the observations with simulation results. PSP observations below 30 solar radii clearly show a positive correlation between proton temperature and wind speed and a negative correlation between electron temperature and wind speed. One year (2019) of WIND data confirm that proton temperature is positively correlated with solar wind speed, but the electron temperature increases with the solar wind speed for slow wind while it decreases with the solar wind speed for fast wind. Using a one-dimensional Alfv\’en-wave-driven solar wind model with different proton and electron temperatures, we for the first time find that if most of the dissipated Alfv\’en wave energy heats the ions instead of electrons, a positive $T_i-V_{SW}$ correlation and a negative $T_e-V_{SW}$ correlation arise naturally. If the electrons gain a small but finite portion of the dissipated wave energy, the $T_e-V_{SW}$ correlation evolves with radial distance to the Sun such that the negative correlation gradually turns positive. The model results show that Alfv\’en waves are one of the possible explanations of the observed evolution of proton and electron temperatures in the solar wind.

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C. Shi, M. Velli, R. Lionello, et. al.
Wed, 4 Jan 23
24/43

Comments: N/A

Misalignment of the outer disk of DK Tau and a first look at its magnetic field using spectropolarimetry [SSA]

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http://arxiv.org/abs/2301.01175


Misalignments between a forming star’s rotation axis and its outer disk axis, although not predicted by standard theories of stellar formation, have been observed in several classical T Tauri stars (cTTs). The low-mass cTTs DK Tau is suspected of being among them. It is also an excellent subject to investigate the interaction between stellar magnetic fields and material accreting from the circumstellar disk, as it presents clear signatures of accretion. The goal of this paper is to study DK Tau’s average line-of-sight magnetic field (Blos) in both photospheric absorption lines and emission lines linked to accretion, using spectropolarimetric observations, as well as to examine inconsistencies regarding its rotation axis. We used data collected with the ESPaDOnS and NARVAL spectropolarimeters, probing two distinct epochs (2010 and 2012). We first determined the stellar parameters, such as effective temperature and v sin i. Next, we removed the effect of veiling from the spectra, then obtained least-squares deconvolution profiles of the absorption lines, before determining the Blos. We also investigated emission lines, the 587.6 nm HeI line and the CaII infrared triplet, as tracers of the magnetic fields present in the accretion shocks. We find that DK Tau experiences accretion onto a magnetic pole at an angle of about 30 degrees from the pole of its rotation axis, with a positive field at the base of the accretion funnels. In 2010 we find a magnetic field of up to 1.77kG, and in 2012 up to 1.99kG. Additionally, using our derived values of period, v sin i and stellar radius, we find a value of 58 degrees (+18)(-11) for the inclination of the stellar rotation axis, which is significantly different from the outer disk axis inclination of 21 degrees given in the literature. We find that DK Tau’s outer disk axis is likely misaligned compared to its rotation axis by 37 degrees.

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M. Nelissen, P. McGinnis, C. Folsom, et. al.
Wed, 4 Jan 23
29/43

Comments: N/A

Three-component modelling of O-rich AGB star winds I. Effects of drift using forsterite [SSA]

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http://arxiv.org/abs/2301.01180


Stellar winds of cool and pulsating asymptotic giant branch (AGB) stars enrich the interstellar medium with large amounts of processed elements and various types of dust. We present a first study on the influence of gas-to-dust drift on ab initio simulations of stellar winds of M-type stars driven by radiation pressure on forsterite particles. Our study is based on our radiation hydrodynamic model code T-800 that includes frequency-dependent radiative transfer, dust extinction based on Mie scattering, grain growth and ablation, gas-to-dust drift using one mean grain size, a piston that simulates stellar pulsations, and an accurate high spatial resolution numerical scheme. To enable this study, we calculated new gas opacities based on the \textsc{exomol} database, and we extended the model code to handle the formation of minerals that may form in M-type stars. We discern effects of drift by comparing drift models to our new and extant non-drift models. Compared to our recent results of C-rich stellar winds, our two new drift models based on an oxygen-rich chemistry show drift velocities that are higher by about a factor ten, that is 310-360 $\text{km}\,\text{s}^{-1}$. Our new drift model mass-loss rates are 8-20 times lower than our own non-drift models, but compared to extant models that use the same stellar parameters, our mass-loss rates are 10-420 times lower. Meanwhile, a comparison of other properties such as the expansion velocity and grain size show similar values. Our results show that the inclusion of gas-to-drift is of fundamental importance in stellar wind models driven by transparent grains such as forsterite. Assuming that the drift velocity is insignificant, properties such as the mass-loss rate may be off from more realistic values by a factor one hundred and more.

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C. Sandin, L. Mattsson, K. Chubb, et. al.
Wed, 4 Jan 23
30/43

Comments: 13 pages, 6 figures, submitted

A search for variable subdwarf B stars in TESS Full Frame Images III. An update on variable targets in both ecliptic hemispheres — contamination analysis and new sdB pulsators [SSA]

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http://arxiv.org/abs/2301.01082


We present an update on the variable star survey performed on the TESS 30 min Full Frame Image (FFI) data reported by our first two papers in this series. This update includes a contamination analysis in order to identify false positives and analysis of the TESS 10 min FFI data collected during Years 3 and 4 of the mission. We clarify the variability status of 2 995 targets identifying 1 403 variable stars. In addition, we spectroscopically classify 24 pre-filtered targets sampled with the 10 min FFI data and discover 11 new sdB pulsators. Future follow-up space- and/or ground-based data of variables reported here, to identify the nature of their variability and reveal spectroscopic parameters of the stars, would complement this work.

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S. Sahoo, A. Baran, H. Worters, et. al.
Wed, 4 Jan 23
33/43

Comments: N/A

Herbig Stars: A Quarter Century of Progress [SSA]

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http://arxiv.org/abs/2301.01165


Herbig Ae/Be stars are young contracting stars on the radiative track in the HR diagram on their way to the main sequence. These stars provide a valuable link between high and low mass stars. Here we review the progress that has been made in our understanding of these fascinating objects and their disks since the last major review on this topic published in 1998. We begin with a general overview of these stars and their properties. We then discuss the accretion of circumstellar material onto these stars. Next we discuss the dust and gas properties of the circumstellar disk before exploring the evidence for planet formation in these disks. We conclude with a brief discussion of future prospects for deepening our understanding of these sources and propose a new working definition of Herbig Ae/Be stars.

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S. Brittain, I. Kamp, G. Meeus, et. al.
Wed, 4 Jan 23
36/43

Comments: 83 pages, 29 figures, to be published in Space Science Reviews

Polarised radio pulsations from a new T dwarf binary [SSA]

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http://arxiv.org/abs/2301.01003


Brown dwarfs display Jupiter-like auroral phenomena such as magnetospheric H$\alpha$ emission and coherent radio emission. Coherent radio emission is a probe of magnetospheric acceleration mechanisms and provides a direct measurement of the magnetic field strength at the emitter’s location, both of which are difficult to access by other means. Observations of the coldest brown dwarfs (spectral types T and Y) are particularly interesting as their magnetospheric phenomena may be very similar to those in gas-giant exoplanets. Here we present 144 MHz radio and infrared adaptive optics observations of the brown dwarf WISEP J101905.63+652954.2 made using the LOFAR and Keck telescopes respectively. The radio data shows pulsed highly circularly polarised emission which yields a rotation rate of $0.32\pm0.03$ hr$^{-1}$. The infrared imaging reveals the source to be a binary with a projected separation of $423.0\pm1.6$ mas between components of spectral type T5.$5\pm0.5$ and T7.$0\pm0.5$. With a simple “toy model” we show that the radio emission can in principle be powered by the interaction between the two dwarfs with a mass-loss rates of at least $25$ times the Jovian value. WISEP J101905.63+652954.2 is interesting because it is the first pulsed methane dwarf detected in a low radio-frequency search. Unlike previous gigahertz-frequency searches that were only sensitive to objects with kiloGauss fields, our low-frequency search is sensitive to surface magnetic fields of $\approx 50$ Gauss and above which might reveal the coldest radio-loud objects down to planetary mass-scales.

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H. Vedantham, T. Dupuy, E. Evans, et. al.
Wed, 4 Jan 23
38/43

Comments: Accepted for publication in A&A

Turbulent Drag Reduction in Magnetohydrodynamic Turbulence and Dynamo from Energy Flux Perspectives [CL]

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http://arxiv.org/abs/2301.01281


In this review, we describe turbulent drag reduction in a variety of flows using a universal framework of energy flux. In a turbulent flow with dilute polymers and magnetic field, the kinetic energy injected at large scales cascades to the velocity field at intermediate scales, as well as to the polymers and magnetic field at all scales. Consequently, the kinetic energy flux, $ \Pi_u(k) $, is suppressed in comparison to the pure hydrodynamic turbulence. We argue that the suppression of $\Pi_u(k)$ is an important factor in the reduction of the inertial force $\langle {\bf u \cdot \nabla u} \rangle$ and \textit{turbulent drag}. This feature of turbulent drag reduction is observed in polymeric, magnetohydrodynamic, quasi-static magnetohydrodynamic, and stably-stratified turbulence, and in dynamos. In addition, it is shown that turbulent drag reduction in thermal convection is due to the smooth thermal plates, similar to the turbulent drag reduction over bluff bodies. In all these flows, turbulent drag reduction often leads to a strong large-scale velocity in the flow.

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M. Verma, M. Sharma and S. Chatterjee
Wed, 4 Jan 23
40/43

Comments: 52 pages, submitted to Reviews of Modern Plasma Physics

Theoretical investigation of the occurrence of tidally excited oscillations in massive eccentric binary systems [SSA]

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http://arxiv.org/abs/2301.00733


Massive and intermediate-mass stars reside in binary systems much more frequently than low-mass stars. Binaries containing massive main-sequence (MS) component(s) are often characterised by eccentric orbits, and can be observed as eccentric ellipsoidal variables (EEVs). The orbital phase-dependent tidal potential acting on the components of EEV can induce tidally excited oscillations (TEOs). We investigate how the history of resonances between the eigenmode spectra of the EEV components and the tidal forcing frequencies depends on the initial parameters of the system. We synthesised 20,000 evolutionary models of the EEVs across the MS. Later, we calculated the eigenfrequencies for each model. We focused only on the $l=2$, $m=0,+2$ modes. Knowing the temporal changes in the orbital parameters of simulated EEVs and the changes of the eigenfrequency spectra for both components, we were able to determine so-called `resonance curves’, which describe the overall chance of a resonance occurring. We analysed the resonance curves by constructing basic statistics for them and analysing their morphology using machine learning methods, including the Uniform Manifold Approximation and Projection tool. The EEV resonance curves from our sample are characterised by striking diversity, including the occurrence of exceptionally long resonances or the absence of resonances for long evolutionary times. Both components may be subject to increased resonance rates as they approach the TAMS. On average, we should observe TEOs more frequently in EEVs containing massive components than intermediate-mass ones. TEOs will be particularly well-pronounced for EEVs with the component(s) close to the TAMS. Given the total number of resonances and their rates, TEOs may play an important role in the transport of angular momentum within massive and intermediate-mass stars (mainly near TAMS).

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P. Kołaczek-Szymański and T. Różański
Tue, 3 Jan 23
1/49

Comments: 24 pages, 15 figures, accepted for publication in A&A

Light Curves of Type IIP Supernovae from Neutrino-driven Explosions of Red Supergiants Obtained by a Semi-analytic Approach [HEAP]

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http://arxiv.org/abs/2301.00359


Type IIP supernovae (SNe IIP) mark the explosive death of red supergiants (RSGs), evolved massive stars with an extended hydrogen envelope. They are the most common supernova type and allow for benchmarking of supernova explosion models by statistical comparison to observed population properties rather than comparing individual models and events. We construct a large synthetic set of SNe IIP light curves (LCs) using the radiation hydrodynamics code \texttt{SNEC} and explosion energies and nickel masses obtained from an efficient semi-analytic model for two different sets of stellar progenitor models. By direct comparison we demonstrate that the semi-analytic model yields very similar predictions as alternative phenomenological explosion models based on one-dimensional simulations. We find systematic differences of a factor of $\mathord{\sim}2$ in plateau luminosities between the two progenitor sets due to different stellar radii, which highlights the importance of the RSG envelope structure as a major uncertainty in interpreting LCs of SNe IIP. A comparison to a volume-limited sample of observed SNe IIP shows decent agreement in plateau luminosity, plateau duration and nickel mass for at least one of the synthetic LC sets. The models, however, do not produce sufficient events with very small nickel mass $M_\mathrm{Ni}<0.01\,M_\odot$ and predict an anticorrelation between plateau luminosity and plateau duration that is not present in the observed sample, a result that warrants further study. Our results suggest that a better understanding of RSG stellar structure is no less important for reliably explaining the light curves of SNe IIP than the explosion physics.

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S. Zha, B. Müller, A. Weir, et. al.
Tue, 3 Jan 23
2/49

Comments: 20 pages, 9 figures, 3 tables

MHD simulation of Solar Eruption from Active Region 11429 Driven by Photospheric Velocity Field [SSA]

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http://arxiv.org/abs/2301.00144


Data-driven simulation is becoming an important approach for realistically characterizing the configuration and evolution of solar active regions, revealing the onset mechanism of solar eruption events and hopefully achieving the goal of accurate space weather forecast, which is beyond the scope of any existing theoretical modelling. Here we performed a full 3D MHD simulation using the data-driven approach and followed the whole evolution process from quasi-static phase to eruption successfully for solar active region NOAA 11429. The MHD system was driven at the bottom boundary by photospheric velocity field, which is derived by the DAVE4VM method from the observed vector magnetograms. The simulation shows that a magnetic flux rope was generated by persistent photospheric flow before the flare onset and then triggered to erupt by torus instability. Our simulation demonstrates a high degree of consistency with observations in the pre-eruption magnetic structure, the time scale of quasi-static stage, the pattern of flare ribbons as well as the time evolution of magnetic energy injection and total unsigned magnetic flux. We further found that an eruption can also be initiated in the simulation as driven by only the horizontal components of photospheric flow, but a comparison of the different simulations indicates that the vertical flow at the bottom boundary is necessary in reproducing more realistically these observed features, emphasizing the importance of flux emergence during the development of this AR.

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X. Wang, C. Jiang and X. Feng
Tue, 3 Jan 23
4/49

Comments: 12 pages, 5 figures

A low-mass hub-filament with double centre revealed in NGC2071-North [GA]

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http://arxiv.org/abs/2301.00481


We present the first analysis in NGC2071-North as a resolved hub-filament featuring a double centre. This $\sim 1.5 \times 1.5$ parsec-scale filament hub contains $\sim$500 $M_\odot$. Seen from Planck, magnetic field lines may have facilitated the gathering of material at this isolated location. The energy balance analysis, supported by infalling gas signatures, reveal that these filaments are currently forming stars. Herschel 100 $\mu$m emission concentrates in the hub, at IRAS 05451+0037 and LkH$\alpha$ 316, and presents diffuse lobes and loops around them. We suggest that such a double centre could be formed, because the converging locations of filament pairs are offset, by 2.3$’$ (0.27 pc). This distance also matches the diameter of a hub-ring, seen in column density and molecular tracers, such as HCO$^+$(1$-$0) and HCN(1$-$0), that may indicate a transition and the connection between the hub and the radiating filaments. We argue that all of the three components of the emission star LkH$\alpha$ 316 are in physical association. We find that a $\sim$0.06 pc-sized gas loop, attached to IRAS 05451+0037, can be seen at wavelengths all the way from Pan-STARRS-i to Herschel-100 $\mu$m. These observations suggest that both protostars at the double hub centre are interacting with the cloud material. In our $^{13}$CO data, we do not seem to find the outflow of this region that was identified in the 80s with much lower resolution.

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V. Könyves, D. Ward-Thompson, Y. Shimajiri, et. al.
Tue, 3 Jan 23
5/49

Comments: 18 pages, 12 figures, accepted for publication in the MNRAS

Data-Constrained Solar Modeling with GX Simulator [SSA]

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http://arxiv.org/abs/2301.00795


To facilitate the study of solar active regions and flaring loops, we have created a modeling framework, the freely distributed GX Simulator IDL package, that combines 3D magnetic and plasma structures with thermal and non-thermal models of the chromosphere, transition region, and corona. The package has integrated tools to visualize the model data cubes, compute multi-wavelength emission maps from them, and quantitatively compare the resulting maps with observations. Its object-based modular architecture, which runs on Windows, Mac, and Unix/Linux platforms, offers capabilities that include the ability to either import 3D density and temperature distribution models, or to assign numerically defined coronal or chromospheric temperatures and densities, or their distributions to each individual voxel. The application integrates FORTRAN and C++ libraries for fast calculation of radio emission (free-free, gyroresonance, and gyrosynchrotron emission) along with soft and hard X-ray and EUV codes developed in IDL. To facilitate the creation of models, we have developed a fully automatic model production pipeline that downloads the required SDO/HMI vector magnetic field data and (optionally) the contextual SDO/AIA images, performs potential or nonlinear force free field extrapolations, populates the magnetic field skeleton with parameterized heated plasma coronal models that assume either steady-state or impulsive plasma heating, and generates non-LTE density and temperature distribution models of the chromosphere that are constrained by photospheric measurements. The standardized models produced by this pipeline may be further customized through a set of interactive tools provided by the graphical user interface. Here we describe the GX Simulator framework and its applications.

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G. Nita, G. Fleishman, A. Kuznetsov, et. al.
Tue, 3 Jan 23
11/49

Comments: N/A

Exploring the Solar Poles: The Last Great Frontier of the Sun [IMA]

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http://arxiv.org/abs/2301.00010


Despite investments in multiple space and ground-based solar observatories by the global community, the Sun’s polar regions remain unchartered territory – the last great frontier for solar observations. Breaching this frontier is fundamental to understanding the solar cycle – the ultimate driver of short-to-long term solar activity that encompasses space weather and space climate. Magnetohydrodynamic dynamo models and empirically observed relationships have established that the polar field is the primary determinant of the future solar cycle amplitude. Models of solar surface evolution of tilted active regions indicate that the mid to high latitude surges of magnetic flux govern dynamics leading to the reversal and build-up of polar fields. Our theoretical understanding and numerical models of this high latitude magnetic field dynamics and plasma flows – that are a critical component of the sunspot cycle – lack precise observational constraints. This limitation compromises our ability to observe the enigmatic kilo Gauss polar flux patches and constrain the polar field distribution at high latitudes. The lack of these observations handicap our understanding of how high latitude magnetic fields power polar jets, plumes, and the fast solar wind that extend to the boundaries of the heliosphere and modulate solar open flux and cosmic ray flux within the solar system. Accurate observation of the Sun’s polar regions, therefore, is the single most outstanding challenge that confronts Heliophysics. This paper argues the scientific case for novel out of ecliptic observations of the Sun’s polar regions, in conjunction with existing, or future multi-vantage point heliospheric observatories. Such a mission concept can revolutionize the field of Heliophysics like no other mission concept has – with relevance that transcends spatial regimes from the solar interior to the heliosphere.

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D. Nandy, D. Banerjee, P. Bhowmik, et. al.
Tue, 3 Jan 23
18/49

Comments: This White Paper was submitted in 2022 to the United States National Academies Solar and Space Physics (Heliophysics) Decadal Survey

Near-infrared evolution of the equatorial ring of SN 1987A [SSA]

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http://arxiv.org/abs/2301.00172


We use adaptive-optics imaging and integral field spectroscopy from the Very Large Telescope, together with images from the \emph{Hubble Space Telescope}, to study the near-infrared (NIR) evolution of the equatorial ring (ER) of SN~1987A. We study the NIR line and continuum flux and morphology over time in order to lay the groundwork for \emph{James Webb Space Telescope} observations of the system. We also study the differences in the interacting ring structure and flux between optical, NIR and other wavelengths, and between line and continuum emission, to constrain the underlying physical processes. Mostly the evolution is similar in the NIR and optical. The morphology of the ER has been skewed toward the west side (with roughly 2/3 of the NIR emission originating there) since around 2010. A steady decline in the ER flux, broadly similar to the MIR and the optical, is ongoing since roughly this time as well. The expansion velocity of the ER hotspots in the NIR is fully consistent with the optical. However, continuum emission forms roughly 70 per cent of the NIR luminosity, and is relatively stronger outside the hotspot-defined extent of the ER than the optical emission or NIR line emission since 2012–2013, suggesting a faster-expanding continuum component. We find that this outer NIR emission can have a significant synchrotron contribution. Even if emission from hot ($\sim$2000~K) dust is dominant within the ER, the mass of this dust must be vanishingly small (a few $\times10^{-12}$~M$\odot$) compared to the total dust mass in the ER ($\gtrsim10^{-5}$~M$\odot$) to account for the observed $HKs$ flux. The location of the NIR continuum emission is different, however, from that of the 180-K dust that dominates in the MIR, and the same hot dust component cannot account for the $J$-band emission.

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T. Kangas, A. Ahola, C. Fransson, et. al.
Tue, 3 Jan 23
20/49

Comments: 17 pages, 16 figures. Submitted to Astronomy & Astrophysics

White Dwarfs with Infrared Excess from LAMOST Data Release 5 [SSA]

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http://arxiv.org/abs/2301.00705


Infrared excess is an important probe of sub-stellar companions and/or debris disks around white dwarfs (WDs). Such systems are still rare for in-depth understanding of their formation and long-term evolution. One of the largest spectroscopic surveys carried out by the Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) recently released more than $3000$ WDs, a significant fraction of which have not undergone excess search. Here we present cross-correlation of LAMOST DR5 WD catalog with the Pan-STARRS, SDSS, UKIDSS, 2MASS, and {\it WISE}. By performing SED (spectral energy distribution) fitting for 846 WDs with $WISE$ detections, we identify 50 candidates with infrared excess, including 7 candidate WD+M dwarf binaries, 31 candidate WD+brown dwarf (BD) binaries and 12 candidate WD+dust disk systems. 8 of the dust disk systems are our new identifications. Utilizing a systematic survey with accurate stellar parameters derived from spectral fitting, our work is an important addition to previous searches for infrared excess from SDSS and {\it Gaia} WDs, and provides a significant ($\gtrsim8\%$) complement to current database of WDs with candidate BD companions and dust disks. The frequencies of WD+BD binaries and WD+dust disk systems are constrained to be $\lesssim3.7\%$ and $\sim1.4\%$, respectively. The properties of candidate dust disk systems are discussed. All of our candidates require follow-up observations for confirmation owing to limited spatial resolution of {\it WISE}.

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L. Wang, X. Zhang, J. Wang, et. al.
Tue, 3 Jan 23
28/49

Comments: 15 pages, 7 figures, 3 tables; accepted for publication in ApJ

Metallicity estimation of MW, SMC and LMC classical Cepheids from the shape of the $V$- and $I$-band light curves [SSA]

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http://arxiv.org/abs/2301.00229


Estimating metallicity of classical Cepheids is of prime importance for studying metallicity effect on stellar evolution, chemical evolution of galaxies, and ultimately its impact on period-luminosity relation used in the extragalactic distance scale. We aim at establishing new empirical relations for estimating the iron content of classical Cepheids for short and long-periods based on Fourier parameters from the $V$-band light curves. We calibrate new interrelations of Fourier parameters to convert $V$-band empirical relations into the $I$-band. Then we apply these relation in $V$ and $I$-bands to Cepheids from Milky Way (MW), Small and Large Magellanic Clouds (SMC and LMC) available in the literature. Last, we map the metallicity distribution in these galaxies for investigating potential application in galactic archeology. These empirical relations in $V$ and $I$ bands are able to derive the mean metallicity of a sample of MW, SMC and LMC Cepheids in agreement with literature values within 1$\sigma$. We also show that these relations are precise enough to reconstruct the radial metallicity gradients within the MW from OGLE data. The empirical relations in the $V$ and $I$ bands calibrated in this paper for short and long-period Cepheids provide a new useful tool to estimate the metallicity of Cepheids which are not accessible by spectroscopy. The calibration can be improved with further high-resolution spectroscopic observations of metal-poor Cepheids and homogeneous photometries in $V$ and $I$ bands.

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V. Hocdé, R. Smolec, P. Moskalik, et. al.
Tue, 3 Jan 23
29/49

Comments: Accepted in A&A, 29 pages, 20 figures

The orbital kinematics of eta Carinae over three periastra with a possible detection of the elusive secondary's motion [SSA]

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http://arxiv.org/abs/2301.00064


The binary eta Carinae is the closest example of a very massive star, which may have formed through a merger during its Great Eruption in the mid-nineteenth century. We aimed to confirm and improve the kinematics using a spectroscopic data set taken with the CTIO 1.5 m telescope over the time period of 2008-2020, covering three periastron passages of the highly eccentric orbit. We measure line variability of H-alpha and H-beta, where the radial velocity and orbital kinematics of the primary star were measured from the H-beta emission line using a bisector method. At phases away from periastron, we observed the He II 4686 emission moving opposite the primary star, consistent with a possible Wolf-Rayet companion, although with a seemingly narrow emission line. This could represent the first detection of emission from the companion.

Read this paper on arXiv…

E. Strawn, N. Richardson, A. Moffat, et. al.
Tue, 3 Jan 23
30/49

Comments: 11 pages, accepted to MNRAS