Category Archives: Solar and Stellar Astrophysics

The 17 April 2021 widespread solar energetic particle event [SSA]

Posted on by

http://arxiv.org/abs/2303.10969


Context. A solar eruption on 17 April 2021 produced a widespread Solar Energetic Particle (SEP) event that was observed by five longitudinally well-separated observers in the inner heliosphere at heliocentric distances of 0.42 to 1 au: BepiColombo, Parker Solar Probe, Solar Orbiter, STEREO A, and near-Earth spacecraft. The event produced relativistic electrons and protons. It was associated with a long-lasting solar hard X-ray flare and a medium fast Coronal Mass Ejection (CME) with a speed of 880 km/s driving a shock, an EUV wave as well as long-lasting radio burst activity showing four distinct type III burst. Methods. A multi-spacecraft analysis of remote-sensing and in-situ observations is applied to attribute the SEP observations at the different locations to the various potential source regions at the Sun. An ENLIL simulation is used to characterize the interplanetary state and its role for the energetic particle transport. The magnetic connection between each spacecraft and the Sun is determined. Based on a reconstruction of the coronal shock front we determine the times when the shock establishes magnetic connections with the different observers. Radio observations are used to characterize the directivity of the four main injection episodes, which are then employed in a 2D SEP transport simulation. Results. Timing analysis of the inferred SEP solar injection suggests different source processes being important for the electron and the proton event. Comparison among the characteristics and timing of the potential particle sources, such as the CME-driven shock or the flare, suggests a stronger shock contribution for the proton event and a more likely flare-related source of the electron event. Conclusions. We find that in this event an important ingredient for the wide SEP spread was the wide longitudinal range of about 110 degrees covered by distinct SEP injections.

Read this paper on arXiv…

N. Dresing, L. Rodríguez-García, I. Jebaraj, et. al.
Tue, 21 Mar 23
55/68

Comments: N/A

3D hydrodynamics simulations of core convection in supermassive main-sequence stars [SSA]

Posted on by

http://arxiv.org/abs/2303.10115


Supermassive stars are Population III stars with masses exceeding $10^4\,M_{\odot}$ that could be the progenitors of the first supermassive black holes. Their interiors are in a regime where radiation pressure dominates the equation of state. In this work, we use the explicit gas dynamics code PPMstar to simulate the hydrogen-burning core of a $10^4\,M_{\odot}$ supermassive main-sequence star. These are the first 3D hydrodynamics simulations of core convection in supermassive stars. We perform a series of ten simulations at different heating rates and on Cartesian grids with resolutions of $768^3$, $1152^3$ and $1728^3$. We examine different properties of the convective flow, including its large-scale morphology, its velocity spectrum and its mixing properties. We conclude that the radiation pressure-dominated nature of the interior does not noticeably affect the behaviour of convection compared to the case of core convection in a massive main-sequence star where gas pressure dominates. Our simulations also offer support for the use of mixing-length theory in 1D models of supermassive stars.

Read this paper on arXiv…

S. Blouin, H. Mao, T. Woods, et. al.
Mon, 20 Mar 23
5/51

Comments: 9 pages, 9 figures, movies at this https URL, accepted for publication in MNRAS

Carbon-Oxygen Phase Separation in MESA White Dwarf Models [SSA]

Posted on by

http://arxiv.org/abs/2303.10110


We enhance the treatment of crystallization for models of white dwarfs (WDs) in the stellar evolution software MESA by implementing carbon-oxygen (C/O) phase separation. The phase separation process during crystallization leads to transport of oxygen toward the center of WDs, resulting in a more compact structure that liberates gravitational energy as additional heating that modestly slows WD cooling timescales. We quantify this cooling delay in MESA C/O WD models over the mass range 0.5-1.0 $M_\odot$, finding delays of 0.5-0.8 Gyr for typical C/O interior profiles. MESA WD cooling timescales including this effect are generally comparable to other WD evolution models that make similar assumptions about input physics. When considering phase separation alongside $^{22}$Ne sedimentation, however, we find that some other sets of WD evolution models may overestimate the cooling delay associated with sedimentation, and this may therefore require a re-evaluation of previously proposed solutions to some WD cooling anomalies. Our implementation of C/O phase separation in the open-source stellar evolution software MESA provides an important tool for building realistic grids of WD cooling models, as well as a framework for expanding on our implementation to explore additional physical processes related to phase transitions and associated fluid motions in WD interiors.

Read this paper on arXiv…

E. Bauer
Mon, 20 Mar 23
6/51

Comments: 14 pages, 9 figures, submitted to ApJ. Comments welcome!

Synthetic photometry for carbon-rich giants. V. Effects of grain-size-dependent dust opacities [SSA]

Posted on by

http://arxiv.org/abs/2303.09984


The properties and the evolution of asymptotic giant branch (AGB) stars are strongly influenced by their mass loss through a stellar wind. This is believed to be caused by radiation pressure due to the absorption and scattering of the stellar radiation by the dust grains formed in the atmosphere. The optical properties of dust are often estimated using the small particle limit (SPL) approximation, and it has been used frequently in modelling AGB stellar winds when performing radiation-hydrodynamics (RHD) simulations. We aim to investigate the effects of replacing the SPL approximation by detailed Mie calculations of the size-dependent opacities for grains of amorphous carbon forming in C-rich AGB star atmospheres. We performed RHD simulations for a large grid of carbon star atmosphere+wind models with different effective temperatures, luminosities, stellar masses, carbon excesses, and pulsation properties. Also, a posteriori radiative transfer calculations for many radial structures (snapshots) of these models were done, resulting in spectra and filter magnitudes. We find, when giving up the SPL approximation, the wind models become more strongly variable and more dominated by gusts, although the average mass-loss rates and outflow speeds do not change significantly; the increased radiative pressure on the dust throughout its formation zone does, however, result in smaller grains and lower condensation fractions (and thus higher gas-to-dust ratios). The photometric K magnitudes are generally brighter, but at V the effects of using size-dependent dust opacities are more complex: brighter for low mass-loss rates and dimmer for massive stellar winds. Given the large effects on spectra and photometric properties, it is necessary to use the detailed dust optical data instead of the simple SPL approximation in stellar atmosphere+wind modelling where dust is formed.

Read this paper on arXiv…

K. Eriksson, S. Höfner and B. Aringer
Mon, 20 Mar 23
25/51

Comments: 14 pages, 24 figures. Accepted for publication in Astronomy \& Astrophysics

Accreting white dwarfs [SSA]

Posted on by

http://arxiv.org/abs/2303.10055


White dwarfs are the most common endpoints of stellar evolution. They are often found in close binary systems in which the white dwarf is accreting matter from a companion star, either via an accretion disc or channelled along the white dwarf magnetic field lines. The nature of this binary depends on the masses and the separation of the two stellar components, as well as other parameters such as the white dwarf magnetic field and the nature of the stars. This chapter looks at the formation of white dwarfs and intrinsic properties, before looking at the different populations of accreting white dwarf binary systems that exist. The chapter covers the characteristics of the various sub-populations and looks at how they evolve. The means to discover and study various sub-classes of accreting white dwarfs in the optical and other bands is discussed, and the role of these systems in the broader astrophysical context is considered. Future missions that will find new systems and new populations are also reviewed. Finally some of the current open questions regarding accreting white dwarfs are presented.

Read this paper on arXiv…

N. Webb
Mon, 20 Mar 23
32/51

Comments: 48 pages, 6 figures, Invited (and accepted) chapter for the Handbook of X-ray and Gamma-ray Astrophysics, Editors: Cosimo Bambi, Andrea Santangelo

A Review of the Mixing Length Theory of Convection in 1D Stellar Modeling [SSA]

Posted on by

http://arxiv.org/abs/2303.09596


We review the application of the one-dimensional Mixing Length Theory (MLT) model of convection in stellar interiors and low-mass stellar evolution. We summarize the history of MLT, present a derivation of MLT in the context of the 1D stellar structure equations, and discuss the physical regimes in which MLT is relevant. We review of attempts to improve and extend the formalism, including to higher dimensions. We discuss the interactions of MLT with other modeling physics and demonstrate the impact of introducing variations in the convective mixing length, {\alpha}MLT, on stellar tracks and isochrones. We summarize the process of performing a solar calibration of {\alpha}MLT and the state-of-the-art on calibrations to non-solar targets. We discuss the scientific implications of changing the mixing length, using recent analyses as demonstration. We review the most prominent successes of MLT and remaining challenges, and we conclude by speculating on the future of this treatment of convection.

Read this paper on arXiv…

M. Joyce and J. Tayar
Mon, 20 Mar 23
33/51

Comments: invited review for MDPI Special Issue “The Structure and Evolution of Stars”

WIYN Open Cluster Study 89. M48 (NGC 2548) 2: Lithium Abundances in the 420 Myr Open Cluster M48 From Giants Through K Dwarfs [SSA]

Posted on by

http://arxiv.org/abs/2303.09783


We consider WIYN/Hydra spectra of 329 photometric candidate members of the 420-Myr-old open cluster M48, and report Lithium detections or upper limits for 234 members and likely members. The 171 single members define a number of notable Li-mass trends, some delineated even more clearly than in Hyades/Praesepe: The giants are consistent with subgiant Li dilution and prior MS Li depletion due to rotational mixing. A dwarfs (8600-7700K) have upper limits higher than the presumed initial cluster Li abundance. Two of five late A dwarfs (7700- 7200K) are Li-rich, possibly due to diffusion, planetesimal accretion, and/or engulfment of hydrogen-poor planets. Early F dwarfs already show evidence of Li depletion seen in older clusters. The Li-Teff trends of the Li Dip (6675-6200K), Li Plateau (6200-6000K), and G and K dwarfs (6000-4000K) are very clearly delineated and are intermediate to those of the 120-Myr-old Pleiades and 650-Myr-old Hyades/Praesepe, which suggests a sequence of Li depletion with age. The cool side of the Li Dip is especially well-defined with little scatter. The Li-Teff trend is very tight in the Li Plateau and early G dwarfs, but scatter increases gradually for cooler dwarfs. These patterns support and constrain models of the universally dominant Li depletion mechanism for FGK dwarfs, namely rotational mixing due to angular momentum loss; we discuss how diffusion and gravity-wave driven mixing may also play roles. For late-G/K dwarfs, faster rotators show higher Li than slower rotators, and we discuss possible connections between angular momentum loss and Li depletion.

Read this paper on arXiv…

Q. Sun, C. Deliyannis, A. Steinhauer, et. al.
Mon, 20 Mar 23
35/51

Comments: 29 pages, 10 figures, 5 tables, accepted for publication in the Astrophysical Journal

The effect of variations in magnetic field direction from turbulence on kinetic-scale instabilities [SSA]

Posted on by

http://arxiv.org/abs/2303.09588


At kinetic scales in the solar wind, instabilities transfer energy from particles to fluctuations in the electromagnetic fields while restoring plasma conditions towards thermodynamic equilibrium. We investigate the interplay between background turbulent fluctuations at the small-scale end of the inertial range and kinetic instabilities acting to reduce proton temperature anisotropy. We analyse in-situ solar wind observations from the Solar Orbiter mission to develop a measure for variability in the magnetic field direction. We find that non-equilibrium conditions sufficient to cause micro-instabilities in the plasma coincide with elevated levels of variability. We show that our measure for the fluctuations in the magnetic field is non-ergodic in regions unstable to the growth of temperature anisotropy-driven instabilities. We conclude that the competition between the action of the turbulence and the instabilities plays a significant role in the regulation of the proton-scale energetics of the solar wind. This competition depends not only on the variability of the magnetic field but also on the spatial persistence of the plasma in non-equilibrium conditions.

Read this paper on arXiv…

S. Opie, D. Verscharen, C. Chen, et. al.
Mon, 20 Mar 23
43/51

Comments: To be published in Astronomy & Astrophysics

The dusty circumstellar environment of Betelgeuse during the Great Dimming as seen by VLTI/MATISSE [SSA]

Posted on by

http://arxiv.org/abs/2303.08892


The ‘Great Dimming’ of the prototypical red supergiant Betelgeuse, which occurred between December 2019 and April 2020, gives us unprecedented insight into the processes occurring on the stellar surface and in the inner wind of this type of star. In particular it may bring further understanding of their dust nucleation and mass loss processes. Here, we present and analyse VLTI/MATISSE observations in the N-band (8 – 13 $\mu$m) taken near the brightness minimum in order to assess the status of the dusty circumstellar environment. We explore the compatibility of a dust clump obscuring the star with our mid-infrared interferometric observations using continuum 3D radiative transfer modelling, and probe the effect of adding multiple clumps close to the star on the observables. We also test the viability of a large cool spot on the stellar surface without dust present in the ambient medium. Using the visibility data, we derive a uniform disk diameter of 59.02 $\pm$ 0.64 mas in the spectral range 8 to 8.75 $\mu$m. We find that both the dust clump and the cool spot models are compatible with the data. Further to this, we note that the extinction and emission of our localised dust clump in the line of sight of the star, directly compensate each other making the clump undetectable in the spectral energy distribution and visibilities. The lack of infrared brightening during the ‘Great Dimming’ therefore does not exclude extinction due to a dust clump as one of the possible mechanisms. The visibilities can be reproduced by a spherical wind with dust condensing at 13 stellar radii and a dust mass-loss rate of (2.1 – 4.9) $\times$ 10$^{-10}$ $\mathit{M}_{\odot} {\rm yr}^{-1}$, however, in order to reproduce the complexity of the observed closure phases, additional surface features or dust clumps would be needed.

Read this paper on arXiv…

E. Cannon, M. Montargès, A. Koter, et. al.
Fri, 17 Mar 23
13/67

Comments: 13 Pages, accepted for publication in A&A

ALMA detection of CO rotational line emission in red supergiant stars of the massive young star cluster RSGC1 — Determination of a new mass-loss rate prescription for red supergiants [SSA]

Posted on by

http://arxiv.org/abs/2303.09385


[Abridged] Aim: We aim to derive a new mass-loss rate prescription for RSGs that is not afflicted with some uncertainties inherent in preceding studies. Methods: We have observed CO rotational line emission towards a sample of RSGs in the open cluster RSGC1 that all are of similar initial mass. The ALMA CO(2-1) line detections allow to retrieve the gas mass-loss rates (Mdot_CO). In contrast to mass-loss rates derived from the analysis of dust spectral features (Mdot_SED), the data allow a direct determination of the wind velocity and no uncertain dust-to-gas correction factor is needed. Results: Five RSGs in RSGC1 have been detected in CO(2-1). The retrieved Mdot_CO values are systematically lower than Mdot_SED. Although only five RSGs in RSGC1 have been detected, the data allow to propose a new mass-loss rate relation for M-type red supergiants that is dependent on luminosity and initial mass. The new mass-loss rate relation is based on the new Mdot_CO values for the RSGs in RSGC1 and on prior Mdot_SED values for RSGs in 4 clusters, including RSGC1. The new Mdot-prescription yields a good prediction for the mass-loss rate of some well-known Galactic RSGs that are observed in multiple CO rotational lines, including alpha Ori, mu Cep and VX Sgr. However, there are indications that a stronger, potentially eruptive, mass-loss process – different than captured by our new mass-loss rate prescription – is occurring during some fraction of the RSG lifetime. Implementing a lower mass-loss rate in evolution codes for massive stars has important consequences for the nature of their end-state. A reduction of the RSG mass-loss rate implies that quiescent RSG mass loss is not enough to strip a single star’s hydrogen-rich envelope. Upon core-collapse such single stars would explode as RSG.

Read this paper on arXiv…

L. Decin, A. Richards, P. Marchant, et. al.
Fri, 17 Mar 23
21/67

Comments: 26 pages, submitted to Astronomy & Astrophysics, minor revisions already implemented

Detection and Characterisation of a Coronal Mass Ejection using Interplanetary Scintillation measurements from the Murchison Widefield Array [SSA]

Posted on by

http://arxiv.org/abs/2303.09134


We have shown previously that the Murchison Widefield Array (MWA), can detect hundreds of Interplanetary Scintillation (IPS) sources simultaneously across a field of view $\sim30^\circ$ in extent. To test if we can use this capability to track heliospheric structures, we undertook a search of 88 hours of MWA IPS data, and identified an observation likely to have a significant Coronal Mass Ejection (CME) in the field of view. We demonstrate that in a single 5-minute MWA observation we are able to localise and image a CME $\sim$33 hours after launch at an elongation of $\sim37^\circ$ from the Sun. We use IPS observables to constrain the kinematics of the CME, and describe how MWA IPS observations can be used in the future to make a unique contribution to heliospheric modelling efforts.

Read this paper on arXiv…

J. Morgan, P. McCauley, A. Waszewski, et. al.
Fri, 17 Mar 23
22/67

Comments: 12 pages, 4 figures. Accepted for publication in “Space Weather” (ISSN:1542-7390)

Quiescence of an Outburst of a Low-Mass Young Stellar Object: LDN1415-IRS [SSA]

Posted on by

http://arxiv.org/abs/2303.09118


LDN1415-IRS, a low-mass young stellar object (YSO) went into an outburst between 2001 and 2006, illuminating a surrounding nebula, LDN1415-Neb. LDN1415-Neb was found to have brightened by I=3.77 mag by April 2006. The optical light curve covering $\sim$ 15.5 years, starting from October 2006 to January 2022, is presented in this study. The initial optical spectrum indicated the presence of winds in the system but the subsequent spectra have no wind indicators. The declining light curve and the absence of the P-Cygni profile in later epoch spectra indicate that the star and nebula system is retrieving back from its outburst state. Two Herbig-Haro objects (HHOs) are positioned linearly with respect to the optical brightness peak of the nebula, probably indicating the circumstellar disk being viewed edge-on. Our recent deep near-infrared (NIR) imaging using TANSPEC has revealed the presence of a nearby star-like source, south of the LDN1415-IRS, at an angular distance of $\sim$ 5.4 arcsec.

Read this paper on arXiv…

K. Singh, D. Ojha, J. Ninan, et. al.
Fri, 17 Mar 23
25/67

Comments: Accepted for publication in the Journal of Astrophysics and Astronomy

Repeating Outbursts from the Young Stellar Object Gaia23bab (= SPICY 97589) [SSA]

Posted on by

http://arxiv.org/abs/2303.09409


The light curve of Gaia23bab (= SPICY 97589) shows two significant ($\Delta G>2$ mag) brightening events, one in 2017 and an ongoing event starting in 2022. The source’s quiescent spectral energy distribution indicates an embedded ($A_V>5$ mag) pre-main-sequence star, with optical accretion emission and mid-infrared disk emission. This characterization is supported by the source’s membership in an embedded cluster in the star-forming cloud DOBASHI 1604 at a distance of $900\pm45$~pc. Thus, the brightening events are probable accretion outbursts, likely of EX Lup-type.

Read this paper on arXiv…

M. Kuhn, R. Benjamin, E. Ishida, et. al.
Fri, 17 Mar 23
30/67

Comments: 4 pages and 1 figure. Submitted to Research Notes of the AAS

Solar center-to-limb variation in Rossiter-McLaughlin and exoplanet transmission spectroscopy [SSA]

Posted on by

http://arxiv.org/abs/2303.09169


Line profiles from spatially unresolved stellar observations consist of a superposition of local line profiles that result from observing the stellar atmosphere under specific viewing angles. Line profile variability caused by stellar magnetic activity or planetary transit selectively varies the weight and/or shape of profiles at individual surface positions. The effect is usually modeled with radiative transfer calculations because observations of spatially resolved stellar surfaces are not available. For the Sun, we recently obtained a broadband spectroscopic atlas of the solar center-to-limb variation (CLV). We use the atlas to study systematic differences between largely used radiative transfer calculations and solar observations. We concentrate on four strong lines useful for exoplanet transmission analysis, and we investigate the impact of CLV on transmission and Rossiter-McLaughlin (RM) curves. Solar models used to calculate synthetic spectra tend to underestimate line core depths but overestimate the effect of CLV. Our study shows that CLV can lead to significant systematic offsets in transmission curves and particularly in RM curves; transmission curves centered on individual lines are overestimated by up to a factor of two by the models, and simulations of RM curves yield amplitudes that are off by up to 5–10\,m\,s$^{-1}$ depending on the line. For the interpretation of transit observations, it is crucial for model spectra that accurately reproduce the solar CLV to become available which, for now, is the only calibration point available.

Read this paper on arXiv…

A. Reiners, F. Yan, M. Ellwarth, et. al.
Fri, 17 Mar 23
38/67

Comments: 10 pages, accepted for publication in A&A, solar spectra library available at this http URL

The First Multiband Photometric Light Curve Solutions of the V Gru Binary System from the Southern Hemisphere [SSA]

Posted on by

http://arxiv.org/abs/2303.09109


The first multiband photometric solutions of the short-period V Gru eclipsing binary from the southern hemisphere is presented in this study. Light curves of the system were observed through BVI filters at the Congarinni Observatory in Australia for 15 nights. In addition to the new ground-based data, we also used the TESS observations in two sectors. We analyzed the light curves of the system using the PHysics Of Eclipsing BinariEs (PHOEBE) 2.4.7 version code to achieve the best accordance with the photometric observations. The solutions suggest that V Gru is a near-contact binary system with q=1.302(81) mass ratio, f1=0.010(23), f2=-0.0.009(21), and i=73.45(38). We considered the two hot spots on the hotter and cooler components for the light curve analysis. We extracted the minima times from the light curves based on the Markov Chain Monte Carlo (MCMC) approach. Using our new light curves, TESS, and additional literature minima, we computed the ephemeris of V Gru. The system’s eclipse timing variation trend was determined using the MCMC method. This system is a good and challenging case for future studies.

Read this paper on arXiv…

M. Tanriver, A. Poro, A. Bulut, et. al.
Fri, 17 Mar 23
45/67

Comments: Accepted by the Research in Astronomy and Astrophysics (RAA) journal

Modeling contact binaries, II. The effect of energy transfer [SSA]

Posted on by

http://arxiv.org/abs/2303.09328


Context. It is common for massive stars to engage in binary interaction. In close binaries, the components can enter a contact phase, where both stars overflow their respective Roche lobes simultaneously. While there exist observational constraints on the stellar properties of such systems, the most detailed stellar evolution models that feature a contact phase are not fully reconcilable with those measurements. Aims. We aim to consistently model contact phases of binary stars in a 1D stellar evolution code. To this end, we develop the methodology to account for energy transfer in the common contact layers. Methods. We implement an approximative model for energy transfer between the components of a contact binary based on the von Zeipel theorem in the stellar evolution code MESA. We compare structure and evolution models with and without this transfer and analyze the implications for the observable properties of the contact phase. Results. Implementing energy transfer helps eliminating baroclinicity in the common envelope between the components of a contact binary, which, if present, would drive strong thermal flows. We find that accounting for energy transfer in massive contact binaries significantly alters the mass ratio evolution and can extend the lifetime of an unequal mass ratio contact system.

Read this paper on arXiv…

M. Fabry, P. Marchant, N. Langer, et. al.
Fri, 17 Mar 23
47/67

Comments: 11 pages, 5 figures. Accepted to A&A

The Empirical Limits of Gyrochronology [SSA]

Posted on by

http://arxiv.org/abs/2303.08830


The promise of gyrochronology is that given a star’s rotation period and mass, its age can be inferred. The reality of gyrochronology is complicated by effects other than ordinary magnetized braking that alter stellar rotation periods. In this work, we present an interpolation-based gyrochronology framework that reproduces the time- and mass-dependent spin-down rates implied by the latest open cluster data, while also matching the rate at which the dispersion in initial stellar rotation periods decreases as stars age. We validate our technique for stars with temperatures of 3800-6200 K and ages of 0.08-2.6 gigayears (Gyr), and use it to reexamine the empirical limits of gyrochronology. In line with previous work, we find that the uncertainty floor varies strongly with both stellar mass and age. For Sun-like stars (5800 K), the statistical age uncertainties improve monotonically from $\pm$38% at 0.2 Gyr to $\pm12$% at 2 Gyr, and are caused by the empirical scatter of the cluster rotation sequences combined with the rate of stellar spin-down. For low-mass K-dwarfs (4200 K), the posteriors are highly asymmetric due to stalled spin-down, and $\pm$1$\sigma$ age uncertainties vary non-monotonically between 10% and 50% over the first few gigayears. High-mass K-dwarfs (5000 K) older than 1.5 Gyr yield the most precise ages, with limiting uncertainties currently set by possible changes in the spin-down rate (12% systematic), the calibration of the absolute age scale (8% systematic), and the width of the slow sequence (4% statistical). An open-source implementation, called gyro-interp, is available online at https://github.com/lgbouma/gyro-interp

Read this paper on arXiv…

L. Bouma, E. Palumbo and L. Hillenbrand
Fri, 17 Mar 23
48/67

Comments: ApJL accepted. Data behind Fig1 are uploaded. Code documentation is at this https URL

Seismological Studies of Pulsating DA White Dwarfs Observed with the Kepler Space Telescope and K2 Campaigns 1-8 [SSA]

Posted on by

http://arxiv.org/abs/2303.08887


All single stars that are born with masses up to 8.5 – 10 $M_\odot$ will end their lives as a white dwarf (WD) star. In this evolutionary stage, WDs enter the cooling sequence, where the stars radiate away their thermal energy, and are basically cooling. As these stars cool, they reach temperatures and conditions that cause the stars to pulsate. Using differential photometry to produce light curves, we can determine the observed periods of pulsation from the WD. We used the White Dwarf Evolution Code (WDEC) to calculate a grid of over one million models with various temperature, stellar mass and mass of helium and hydrogen layers, and calculated their theoretical pulsation periods. In this paper, we describe our approach to WD asteroseismology using WDEC models and we present seismological studies for 29 observed DAVs in the Kepler and K2 datasets, 25 of which have never been analyzed using these observations, and 19 of which have never been seismically analyzed in any capacity before. Learning about the internal structure of WDs place important constraints on the WD cooling sequence and our overall understanding of stellar evolution for low mass stars.

Read this paper on arXiv…

W. Hall, B. Castanheira and A. Bischoff-Kim
Fri, 17 Mar 23
58/67

Comments: 22 pages, 9 Tables and 12 Figures, ApJ accepted

Physics-based model of solar wind stream interaction regions: Interfacing between Multi-VP and 1D MHD for operational forecasting at L1 [SSA]

Posted on by

http://arxiv.org/abs/2303.09221


Our current capability of space weather prediction in the Earth’s radiation belts is limited to only an hour in advance using the real-time solar wind monitoring at the Lagrangian L1 point. To mitigate the impacts of space weather on telecommunication satellites, several frameworks were proposed to advance the lead time of the prediction. We develop a prototype pipeline called “Helio1D” to forecast ambient solar wind conditions (speed, density, temperature, tangential magnetic field) at L1 with a lead time of 4 days. This pipeline predicts Corotating Interaction Regions (CIRs) and high-speed streams that can increase high-energy fluxes in the radiation belts. The Helio1D pipeline connects the Multi-VP model, which provides real-time solar wind emergence at 0.14 AU, and a 1D MHD model of solar wind propagation. We benchmark the Helio1D pipeline for solar wind speed against observations for the intervals in 2004 – 2013 and 2017 – 2018. We developed a framework based on the Fast Dynamic Time Warping technique that allows us to continuously compare time-series outputs containing CIRs to observations to measure the pipeline’s performance. In particular, we use this framework to calibrate and improve the pipeline’s performance for operational forecasting. To provide timing and magnitude uncertainties, we model several solar wind conditions in parallel, for a total of 21 profiles corresponding to the various virtual targets including the Earth. This pipeline can be used to feed real-time, daily solar wind forecasting that aims to predict the dynamics of the inner magnetosphere and the radiation belts.

Read this paper on arXiv…

R. Kieokaew, R. Pinto, E. Samara, et. al.
Fri, 17 Mar 23
60/67

Comments: 24 pages, 9 figures. The appendix is available upon request

Multifrequency microwave imaging of weak transients from the quiet solar corona [SSA]

Posted on by

http://arxiv.org/abs/2301.07840


Understanding the dynamics of the quiet solar corona is important for answering key questions including the coronal heating problem. Multiple studies have suggested small-scale magnetic reconnection events may play a crucial role. These reconnection events are expected to involve accelerating electrons to suprathermal energies, which can then produce nonthermal observational signatures. However, due to the paucity of sensitive high-fidelity observations capable of probing these nonthermal signatures, most studies were unable to quantify their nonthermal nature. Here we use joint radio observations from the Very Large Array (VLA) and the Expanded Owens Valley Solar Array (EOVSA) to detect transient emissions from the quiet solar corona in the microwave (GHz) domain. While similar transients have been reported in the past, their nonthermal nature could not be adequately quantified due to the unavailability of broadband observations. Using a much larger bandwidth available now with the VLA and EOVSA, in this study, we are able to quantify the nonthermal energy associated with two of these transients. We find that the total nonthermal energy associated with some of these transients can be comparable to or even larger than the total thermal energy of a nanoflare, which underpins the importance of nonthermal energy in the total coronal energy budget.

Read this paper on arXiv…

S. Mondal, B. Chen and S. Yu
Fri, 20 Jan 23
9/72

Comments: Submitted to ApJ

An XMM-Newton view of the Symbiotic Stars HM Sge, NQ Gem, and PU Vul [SSA]

Posted on by

http://arxiv.org/abs/2301.08191


We present the analysis of archival XMM-Newton observations of the symbiotic stars (SySts) HM Sge, NQ Gem, and PU Vul. The EPIC-pn spectra reveal the presence of emission lines and spectral modeling reveal unprecedented characteristics. For instance, the best fit to the EPIC-pn spectrum of the $\beta$-type SySt PU Vul reveals the presence of two plasma components. We report the discovery of an extremely soft spectral component in the EPIC-pn spectrum of the $\beta$-type Syst HM Sge which we suggest is produced by periodic mass ejections such as jets. We suggest that a simple $\beta$-type classification no longer applies to HM Sge. Finally, the spectrum of the $\beta/\delta$-type SySt NQ Gem can not be fitted by a two-temperature plasma model as performed by previous authors. The model requires extra components to fit the 1.0–4.0 keV energy range. More sophisticated models to $\beta/\delta$-type SySt are needed in order to peer into the accretion process from such systems.

Read this paper on arXiv…

J. Toalá, M. Botello and L. Sabin
Fri, 20 Jan 23
21/72

Comments: 6 pages, 2 Tables, 2 Figures; Submitted to ApJ

Stereoscopic Observation of Simultaneous Longitudinal and Transverse Oscillations in a Single Filament Driven by Two-sided-loop Jet [SSA]

Posted on by

http://arxiv.org/abs/2301.07989


We report the first observations of simultaneous large-amplitude longitudinal and transverse oscillations of a quiescent filament trigged by a two-sided-loop jet formed by the magnetic reconnection between the filament and an emerging loop in the filament channel, recorded by the Solar Dynamics Observatory and the Solar TErrestrial RElations Observatory. The north arm of the jet firstly pushed the filament mass moving northwardly along the magnetic field lines consisting of the coronal cavity, then some elevated filament mass fell back and started to oscillate longitudinally at the bottom of the cavity (i.e., the magnetic dip). The northernmost part of the filament also showed transverse oscillation simultaneously. The amplitude and period of the longitudinal (transverse) oscillation are 12.96 (2.99) Mm and 1.18 (0.33) hours, respectively. By using the method of filament seismology, the radius of curvature of the magnetic dip is about 151 Mm, consistent with that obtained by the 3D reconstruction (166 Mm). Using different physical parameters of the observed longitudinal and transverse oscillations, the magnetic field strength of the filament is estimated to be about 23 and 21 Gauss, respectively. By calculating the energy of the moving filament mass, the minimum energy of the jet is estimated to be about 1.96 x 10^28 erg. We conclude that the newly formed jet can not only trigger simultaneous longitudinal and transverse oscillations in a single filament, but also can be used as a seismology tool for diagnosing filament information, such as the magnetic structure, magnetic field strength, and magnetic twists.

Read this paper on arXiv…

S. Tan, Y. Shen, X. Zhou, et. al.
Fri, 20 Jan 23
26/72

Comments: 9 pages, 7 figures, accept by MNRAS

Photometric Calibrations of M-dwarf Metallicity with Markov Chain Monte Carlo and Bayesian Inference [SSA]

Posted on by

http://arxiv.org/abs/2301.08036


Knowledge of stellar atmospheric parameters ($T_{\rm eff}$, $\log{g}$, [Fe/H]) of M dwarfs can be used to constrain both theoretical stellar models and Galactic chemical evolutionary models, and guide exoplanet searches, but their determination is difficult due to the complexity of the spectra of their cool atmospheres. In our ongoing effort to characterize M dwarfs, and in particular their chemical composition, we carried out multiband photometric calibrations of metallicity for early- and intermediate-type M dwarfs. The third Gaia data release provides high-precision astrometry and three-band photometry. This information, combined with the 2MASS and CatWISE2020 infrared photometric surveys and a sample of 4919 M dwarfs with metallicity values determined with high-resolution spectroscopy by The Cannon and APOGEE spectra, allowed us to study the effect of the metallicity in color-color and color-magnitude diagrams. We divided this sample into two subsamples: we used 1000 stars to train the calibrations with Bayesian statistics and Markov Chain Monte Carlo techniques, and the remaining 3919 stars to check the accuracy of the estimations. We derived several photometric calibrations of metallicity applicable to M dwarfs in the range of $-0.45\leq\text{[Fe/H]}\leq +0.45$ dex and spectral types down to M5.0 V that yield uncertainties down to the $0.10$ dex level. Lastly, we compared our results with other photometric estimations published in the literature for an additional sample of 46 M dwarfs in wide binary systems with FGK-type primary stars, and found a great predictive performance.

Read this paper on arXiv…

C. Duque-Arribas, D. Montes, H. Tabernero, et. al.
Fri, 20 Jan 23
31/72

Comments: Accepted for publication in ApJ, 24 pages, 14 figures and 7 tables

Where are the missing symbiotic stars? Uncovering hidden Symbiotic Stars in public catalogues [SSA]

Posted on by

http://arxiv.org/abs/2301.08201


Theoretical predictions of the population of Galactic symbiotic stars (SySts) are highly inconsistent with the current known population. Despite intense effort over the past decades, observations are still far below the predictions. The majority of known SySts so far are identified based on selection criteria established in the optical regime. The recent discovery of SU Lyn with very faint optical emission lines uncloaked a subgroup of SySts with accreting-only white dwarfs. In this particular case, the luminous red giant may overshadow the dimmed white dwarf companion. A new approach to search for this subgroup of SySts is presented, employing GALEX UV and 2MASS/AllWISE IR photometry. The FUV-NUV colour index is an indicator, direct or indirect, for the presence of hot compact companions. The cross-match of the Catalogue of Variable Stars III obtained from the All-Sky Automated Survey for SuperNovae with the GALEX, 2MASS and AllWISE catalogues result in a sample of 814 potential SySt candidates. From them, 105 sources have photometric measurements from both FUV and NUV bands and 35 exhibit FUV-NUV<1, similar to what it is expected from known SySts. Five known SySts are recovered, while two new genuine SySts are discovered in spectroscopic follow-up observations after the detection of the typical emission lines.

Read this paper on arXiv…

S. Akras
Fri, 20 Jan 23
48/72

Comments: 11 pages, 5 figures, 1 table, accepted for Publication in MNRAS

Texture of average solar photospheric flows and the donut-like pattern [SSA]

Posted on by

http://arxiv.org/abs/2301.07988


Detailed knowledge of surface dynamics is one of the key points in understanding magnetic solar activity. The motions of the solar surface, to which we have direct access via the observations, tell us about the interaction between the emerging magnetic field and the turbulent fields.
The flows computed with the coherent structure tracking (CST) technique on the whole surface of the Sun allow for the texture of the velocity modulus to be analyzed and for one to locate the largest horizontal flows and determine their organization. The velocity modulus maps show structures more or less circular and closedwhich are visible at all latitudes; here they are referred to as donuts. They reflect the most active convective cells associated with supergranulation. These annular flows are not necessarily joined as would seem to indicate the divergence maps. The donuts have identical properties (amplitude, shape, inclination, etc.) regardless of their position on the Sun. The kinematic simulation of the donuts’ outflow applied to passive scalar (corks) indicates the preponderant action of the selected donuts which are, from our analysis, one of the major actors for the magnetic field diffusion on the quiet Sun. The absence of donuts in the magnetized areas (plages) indicates the action of the magnetic field on the strongest supergranular flows and thus modifies the diffusion of the magnetic field in that location. The detection of the donuts is a way to locate in the quiet Sun the vortex and the link with the jet, blinkers, coronal bright points (campfires), or other physical structures. Likewise, the study of the influence of donuts on the evolution of active events, such as the destruction of sunspots, filament eruptions, and their influences on upper layers via spicules and jets, could be done more efficiently via the detection of that structures.

Read this paper on arXiv…

T. Roudier, J. Ballot, J. Malherbe, et. al.
Fri, 20 Jan 23
51/72

Comments: 14 pages, 17 figures

BD+30$^\circ$549: young helium-weak silicon star in NGC 1333 star-forming region [SSA]

Posted on by

http://arxiv.org/abs/2301.07856


We present results of the spectroscopic study of the chemically peculiar star BD+30$^\circ$549 which is bona-fide member of young NGC 1333 star forming region. We found that the star possesses negligible rotation and helium-weak spectroscopic pattern with strongly enhanced Si II and Si III lines. The fundamental parameters of the star $T_{eff}$=13100~K and $\log (L/L_{\odot})$=2.1 indicate its age of about 2.7 Myr and position on the Hertzsprung-Russell diagram at the end of the Pre-Main Sequence evolutionary track, close to the Zero Age Main Sequence. Abundance analysis reveals the modest deficit of almost all elements with exception of Si, Fe, Ca and P which are overabundant. We performed the non-LTE calculations for Si II/Si III, Mg II and Ca II in order to check the influence of departures from LTE on line formation. Non-LTE calculations lead to much better reproduction of individual silicon line profiles, but does not completely remove the abundance discrepancy between Si II and Si III lines. We also investigate the effects of possible chemical stratification in BD+30$^\circ$549. We suspect that the “Si II/Si III anomaly”, observed in BD+30$^\circ$549 spectrum arises under the combined action of the vertical and horizontal abundance gradients and non-LTE effects. We suppose that evolutionary status and phenomena observed in BD+30$^\circ$549 indicate that conditions favorable for the selective diffusion and formation of the surface chemical composition peculiarities (slow rotation and stabilization of the atmosphere) can be built up already at the Pre-Main Sequence phase.

Read this paper on arXiv…

I. Potravnov, L. Mashonkina and T. Ryabchikova
Fri, 20 Jan 23
52/72

Comments: N/A

Structure and evolution of a tidally heated star [SSA]

Posted on by

http://arxiv.org/abs/2301.07878


The shearing motion of tidal flows that are excited in non-equilibrium binary stars transform kinetic energy into heat via a process referred to as tidal heating. In this paper we aim to explore the way tidal heating affects the stellar structure. We used the TIDES code, which solves the equations of motion of the three-dimensional (3D) grid of volume elements that conform multiple layers of a rotating binary star to obtain an instantaneous value for the angular velocity, $\omega”$, as a function of position in the presence of gravitational, centrifugal, Coriolis, gas pressure, and viscous forces. The released energy, $\dot{E,}$ was computed using a prescription for turbulent viscosity that depends on the instantaneous velocity gradients. The $\dot{E}$ values for each radius were injected into a MESA stellar structure calculation. The method is illustrated for a 1.0+0.8 M$_\odot$ binary system, with an orbital period of $P$=1.44d and departures from synchronous rotation of 5% and 10%. We find that heated models have a larger radius and surface luminosity, a smaller surface convection zone, and lower nuclear reaction rates than the equivalent standard stellar models, and their evolutionary tracks extend to higher temperatures. The magnitude of these effects depends on the amount of injected energy, which, for a fixed set of stellar, rotation and orbital parameters, depends on the perturbed star’s density structure and turbulent viscosity. Tidal heating offers a possible alternative for describing phenomena such as bloated or overluminous binary components, age discrepancies, and aspherical mass ejection, as well as the extended main sequence turnoff in clusters. However, establishing its actual role requires 3D stellar structure models commensurate with the nonspherically symmetric properties of tidal perturbations.

Read this paper on arXiv…

D. Estrella-Trujillo, S. Arthur, G. Koenigsberger, et. al.
Fri, 20 Jan 23
56/72

Comments: 16 pages, 7 figures, appendix with 9 figures, A&A in Press

Characterising fast-time variations in the hard X-ray time profiles of solar flares using Solar Orbiter's STIX [SSA]

Posted on by

http://arxiv.org/abs/2301.08040


Aims: The aim of this work is to develop a method to systematically detect and characterise fast-time variations ($\gtrsim 1$s) in the non-thermal hard X-ray (HXR) time profiles of solar flares using high-resolution data from Solar Orbiter’s Spectrometer/Telescope for Imaging X-rays (STIX).
Methods: The HXR time profiles were smoothed using Gaussian Process (GP) regression. The time profiles were then fitted with a linear combination of Gaussians to decompose the time profile. From the Gaussian decomposition, key characteristics such as the periodicity, full width at half maximum (FWHM), time evolution, and amplitude can be derived.
Results: We present the outcome of applying this method to four M and X GOES-class flares from the first year of Solar Orbiter science operations. The HXR time profiles of these flares were decomposed into individual Gaussians and their periods were derived. The quality of fit is quantified by the standard deviation of the residuals (difference between observed and fitted curve, normalised by the error on the observed data), for which we obtain $\leq 1.8$ for all flares presented. In this work, the first detection of fast-time variations with Solar Orbiter’s STIX instrument has been made on timescales across the range of 4-128s.
Conclusions: A new method for identifying and characterising fast-time variations in the non-thermal HXR profiles of solar flares has been developed, in which the time profiles are fit with a linear combination of Gaussian bursts. The opportunity to study time variations in flares has greatly improved with the new observations from STIX on Solar Orbiter.

Read this paper on arXiv…

H. Collier, L. Hayes, A. Battaglia, et. al.
Fri, 20 Jan 23
60/72

Comments: 12 pages, 10 figures, A&A journal

Plasma broadening of autoionizing resonances [SSA]

Posted on by

http://arxiv.org/abs/2301.07734


A general formulation is developed to demonstrate that atomic autoionizing (AI) resonances are broadened and shifted significantly due to plasma effects across bound-free continua. The theoretical and computational method presented accounts for broadening mechanisms: electron collisional, ion microfields (Stark), thermal Doppler, core excitations, and free-free transitions. {\it Extrinsic} plasma broadening redistributes and shifts AI resonance strengths while broadly preserving naturally {\it intrinsic} asymmetries of resonance profiles. Integrated oscillator strengths are conserved as resonance structures dissolve into continua with increasing electron density. As exemplar, the plasma attenuation of photoionization cross sections computed using the R-matrix method is studied in neon-like Fe~XVII in a critical range $N_e = 10^{21-24}$cc along isotherms $T = 1-2 \times 10^6$K, and its impact on Rosseland Mean opacities. The energy-temperature-density dependent cross sections would elicit and introduce physical features in resonant processes in photoionization, \eion excitation and recombination. The method should be generally applicable to atomic species in high-energy-density (HED) sources such as fusion plasmas and stellar interiors.

Read this paper on arXiv…

A. Pradhan
Fri, 20 Jan 23
62/72

Comments: 5 pages, 3 figures

Core-envelope decoupling drives radial shear dynamos in cool stars [SSA]

Posted on by

http://arxiv.org/abs/2301.07716


Differential rotation is thought to be responsible for the dynamo process in stars like our Sun, driving magnetic activity and star spots. We report that star spot measurements in the Praesepe open cluster are strongly enhanced only for stars which depart from standard models of rotational evolution. A decoupling of the spin down history between the core and envelope explains both the activity and rotation anomalies: surface rotational evolution is stalled by interior angular momentum redistribution, and the resultant radial shears enhance star spot activity. These anomalies provide evidence for an evolving front of shear-enhanced activity affecting the magnetic and rotational evolution of cool stars and the high-energy environments of their planetary companions for hundreds of millions to billions of years on the main sequence.

Read this paper on arXiv…

L. Cao, M. Pinsonneault and J. Saders
Fri, 20 Jan 23
63/72

Comments: 12 pages, 8 figures. Submitted to ApJ Letters

A disk-wind driving the rotating molecular outflow in CB 26 [SSA]

Posted on by

http://arxiv.org/abs/2301.07877


We present 12CO (J=2-1) sensitive molecular line and 1.3 mm continuum observations made with the Submillimeter Array (SMA) of the bipolar outflow associated with the young star located in the Bok globule known as CB 26. The SMA observations were carried out in its extended configuration allowing us to study the kinematics and structure of the outflow with about 1 arcsec or 140 au resolution. We find that the dusty and edge-on circumstellar disk related with the outflow has an projected spatial (deconvolved) size of 196 au x 42 au with a total (gas and dust) mass of 0.031 Msun. We estimated a dynamical mass for the central object of 0.66 Msun, and the mass of the molecular outflow of 5×10-5 Msun. The observations confirm that the outflow rotation has a similar orientation to that of the edge-on disk. For the outflow, we find that the following quantities: the rotation velocity, the specific angular momentum, and the launching radius, decrease with the height above mid-plane, as observed in other molecular rotating outflows. The radius, and expansion velocity also increase with the height above the disk midplane. Estimations for the outflow linear momentum rate, the outflow angular momentum rate, and the accretion luminosity seem to be well explained by a disk wind present in CB26.

Read this paper on arXiv…

J. López-Vázquez, L. Zapata and C. Lee
Fri, 20 Jan 23
71/72

Comments: 9 pages, 8 figures

Exploring the Temporal Variation of the Solar Quadrupole Moment J2 [SSA]

Posted on by

http://arxiv.org/abs/2301.07506


Recently, Rozelot & Eren pointed out that the first solar gravitational moment (J2) might exhibit a temporal variation. The suggested explanation is through the temporal variation of the solar rotation with latitude. This issue is deeper developed due to an accurate knowledge of the long-term variations in solar differential rotation regarding solar activity. Here we analyze solar cycles 12-24, investigating the long-term temporal variations in solar differential rotation. It is shown that J2 exhibits a net modulation over the 13 studied cycles of approximately (89.6 +- 0.1) yr, with a peak-to-peak amplitude of approximately 0.1 x 10-7 for a reference value of 2.07 x 10-7). Moreover, J2 exhibits a positive linear trend in the period of minima solar activity (sunspot number up to around 40) and a marked declining trend in the period of maxima (sunspot number above 50). In absolute magnitude, the mean value of J2 is more significant during periods of minimum than in periods of maximum. These findings are based on observational results that are not free of errors and can be refined further by considering torsional oscillations for example. They are comforted by identifying a periodic variation of the J2 term evidenced through the analysis of the perihelion precession of planetary orbits either deduced from ephemerides or computed in the solar equatorial coordinate system instead of the ecliptic coordinate one usually used.

Read this paper on arXiv…

S. Eren and J. Rozelot
Thu, 19 Jan 23
3/100

Comments: 7 pages, 5 figures

Data-Driven Radiative Magnetohydrodynamics Simulations with the MURaM code [SSA]

Posted on by

http://arxiv.org/abs/2301.07621


We present a method of conducting data-driven simulations of solar active regions and flux emergence with the MURaM radiative magnetohydrodynamics (MHD) code. The horizontal electric field derived from the full velocity and magnetic vectors, is implemented at the photospheric (bottom) boundary to drive the induction equation. The energy equation accounts for thermal conduction along magnetic fields, optically-thin radiative loss, and heating of coronal plasma by viscous and resistive dissipation, which allows for a realistic presentation of the thermodynamic properties of coronal plasma that are key to predicting the observational features of solar active regions and eruptions. To validate the method, the photospheric data from a comprehensive radiative MHD simulation of solar eruption (the ground truth) are used to drive a series of numerical experiments. The data-driven simulation reproduces the accumulation of free magnetic energy over the course of flux emergence in the ground truth with an error of 3\%. The onset time is approximately 8\,min delayed compared to the ground truth. However, a precursor-like signature can be identified at the correct onset time. The data-driven simulation captures key eruption-related emission features and plasma dynamics of the ground truth flare over a wide temperature span from $\log_{10}T{=}4.5$ to $\log_{10}T{>}8$. The evolution of the flare and coronal mass ejection as seen in synthetic extreme ultraviolet images is also reproduced with high fidelity. The method helps to understand the evolution of magnetic field in a more realistic coronal environment and to link the magnetic structures to observable diagnostics.

Read this paper on arXiv…

F. Chen, M. Cheung, M. Rempel, et. al.
Thu, 19 Jan 23
10/100

Comments: 34 pages, 23 figures, submitted to ApJ

Variation of small scale magnetic fields over a century using Ca-K images as proxy [SSA]

Posted on by

http://arxiv.org/abs/2301.07350


A combined uniform and long-time series of Ca-K images from the Kodaikanal Observatory (KO), Mount Wilson Observatory (MWO), and Mauna Loa Solar Observatory (MLSO) were used to identify and study the Ca-K small-scale features and their solar cycle variations over a century. The small scale features are classified into three distinct categories: enhanced network (EN), active network (AN), and quiet network (QN). All these features show that their areas vary according to the 11-year solar cycle. The relative amplitude of the Ca-K network variations agree with that of the sunspot cycle. The total area of these small-scale features varies from about 5% during the minimum phase of the solar cycle to about 20% during its maximum phase. Considering the average intensity and the amplitude of their area variations, we find that the total contribution of EN, AN and QN to the irradiance variation of the Sun is about 3%.

Read this paper on arXiv…

J. Singh, M. Priyal, B. Ravindra, et. al.
Thu, 19 Jan 23
17/100

Comments: Submitted article in RAA. It is under review. 15 pages, 8 figures

Parametric instability in warped astrophysical discs: growth, saturation and feedback [SSA]

Posted on by

http://arxiv.org/abs/2301.07176


Attempts to understand the dynamics of warped astrophysical discs have garnered significant attention, largely motivated by the growing catalogue of observed distorted systems. Previous studies have shown that the evolution of the warp is crucially regulated by the internal flow fields established by the undulating geometry. These are typically modelled as laminar horizontal, shearing flows which oscillate back and forth at approximately the orbital frequency. However this shearing motion is known to be susceptible to a hydrodynamic, parametric instability of inertial waves which might modify the warped dynamics. Whilst the linear growth phase is well understood, the subsequent nonlinear saturation combined with the self-consistent feedback onto the warp has not been studied. In this work, we implement a novel numerical setup using the recent ring model framework of Fairbairn and Ogilvie, within the Lagrangian code GIZMO. We formally identify several locally growing modes in the simulation, as predicted by a three-mode coupling analysis of the instability, and find decent agreement with the theoretical growth rates. We understand the saturation mechanism as a wave breaking process which suppresses the growth of shorter wavelength parametric couplings first, whilst allowing the longest mode to dominate the final quasi-steady, wavelike turbulence. The Reynolds stresses, transporting energy from the warp to the small scales, can be effectively modelled using a time-dependent, anisotropic viscous alpha model which closely captures the amplitude and phase evolution of the warp. Consequently, this model might help inform future global studies which are commonplace but typically don’t resolve the parametric instability.

Read this paper on arXiv…

C. Fairbairn and G. Ogilvie
Thu, 19 Jan 23
40/100

Comments: Accepted MNRAS, 22 pages, 17 figures

The orbits of visual binary and multiple stars obtained by the Apparent Motion Parameters method during the last 40 years [SSA]

Posted on by

http://arxiv.org/abs/2301.07602


Summed many years of work at Pulkovo, the orbits of 67 wide pairs of visual double and multiple stars (included in 64 systems) which were obtained by the Apparent Motion Parameters (AMP) method are presented. This short arc orbit determination method is based on the most reliable astrometric and astrophysical data corresponding to one instant of time. The rest of the observations accumulated in the world serve to control the quality of the orbit and refine some parameters. All early determined AMP-orbits were compared with new observations, some of them were recalculated, new ones were added. For the stars of Pulkovo program of observations with a 26-inch refractor, the Gaia DR2 data were analised. Based on these data, the orbits of 16 stars were calculated. In 20 cases from 67, the quasi-instant motion according to the Gaia DR2 data at the instant 2015.5 contradicts the motion according to all-world observations. A possible reason is the presence of inner subsystems. The orientation of the obtained orbits in the galactic coordinate system is also given.

Read this paper on arXiv…

L. Romanenko, O. Kiyaeva, I. Izmailov, et. al.
Thu, 19 Jan 23
42/100

Comments: 12 pages

First total recovery of Sun global Alfven resonance: least-squares spectra of decade-scale dynamics of N-S-separated fast solar wind reveal solar-type stars act as revolving-field magnetoalternators [SSA]

Posted on by

http://arxiv.org/abs/2301.07219


The Sun reveals itself in the 385.8-2.439-nHz band of polar ({\phi}Sun>|70{\deg}|) fast (>700 km s^-1) solar wind’s decade-scale dynamics as a globally completely vibrating, revolving-field magnetoalternator rather than a proverbial engine. Thus North-South separation of 1994-2008 Ulysses <10 nT wind polar samplings spanning ~1.6 10^7-2.5 10^9-erg base energies reveals Gauss-Vanicek spectral signatures of an entirely >99%-significant Sun-borne global sharp Alfven resonance (AR), Pi=PS/i, imprinted into the winds to the order n=100+ and co-triggered by the PS=~11-yr Schwabe global mode northside, its ~10-yr degeneration equatorially, and ~9-yr degeneration southside. The Sun is a typical ~3-dB-attenuated ring-system of differentially rotating and contrarily (out-of-phase) vibrating conveyor belts and layers with a continuous spectrum and resolution (<81.3 nHz (S), <55.6 nHz (N)) in lowermost frequencies (<2 {\mu}Hz in most modes). AR is accompanied by an also sharp symmetrical antiresonance P(-) whose both N/S tailing harmonics P(-17) are the well-known PR=~154-day Rieger period dominating planetary dynamics and space weather. Unlike a resonating motor restrained from separating its casing, the freely resonating Sun exhausts the wind in an axial shake-off beyond L1 at highly coherent discrete wave modes generated in the Sun, so to understand solar-type stars, only global decadal scales matter. The result verified against remote data and the experiment, so it instantly replaces dynamo with magnetoalternator and advances Standard Stellar Models, improving fundamental understanding of billions of trillions of solar-type stars. Gauss-Vanicek spectral analysis revolutionizes planetary & space sciences by rigorously simulating multiple spacecraft or fleet formations from a single spacecraft and physics by directly computing nonlinear global dynamics (rendering spherical approximation obsolete).

Read this paper on arXiv…

M. Omerbashich
Thu, 19 Jan 23
51/100

Comments: 31 pages, 7 figures, 3 tables

Quasi-periodic Variations of Coronal Mass Ejections with Different Angular Widths [SSA]

Posted on by

http://arxiv.org/abs/2301.07379


Coronal mass ejections (CMEs) are energetic expulsions of organized magnetic features from the Sun. The study of CME quasi-periodicity helps establish a possible relationship between CMEs, solar flares, and geomagnetic disturbances. We used the angular width of CMEs as a criterion for classifying the CMEs in the study. Based on 25 years of observational data, we systematically analyzed the quasi-periodic variations corresponding to the CME occurrence rate of different angular widths in the northern and southern hemispheres, using frequency and time-frequency analysis methods. There are various periods for CMEs of different angular widths: 9 months, 1.7 years, and 3.3-4.3 years. Compared with previous studies based on the occurrence rate of CMEs, we obtained the same periods of 1.2(+-0.01) months, 3.1(+-0.04) months, ~6.1(+-0.4) months, 1.2(+-0.1) years, and 2.4(+-0.4) years. We also found additional periods of all CMEs that appear only in one hemisphere or during a specific solar cycle. For example, 7.1(+-0.2) months and 4.1(+-0.2) years in the northern hemisphere, 1(+-0.004) months, 5.9(+-0.2) months, 1(+-0.1) years, 1.4(+-0.1) years, and 2.4(+-0.4) years in the southern hemisphere, 6.1(+-0.4) months in solar cycle 23 (SC23) and 6.1(+-0.4) months, 1.2(+-0.1) years, and 3.7(+-0.2) years in solar cycle 24 (SC24). The analysis shows that quasi-periodic variations of the CMEs are a link among oscillations in coronal magnetic activity, solar flare eruptions, and interplanetary space.

Read this paper on arXiv…

X. Li, H. Deng, F. Wang, et. al.
Thu, 19 Jan 23
53/100

Comments: 18 pages, 8 figures, 4 tables, Accepted by APJ

No evidence for synchronization of the solar cycle by a "clock" [SSA]

Posted on by

http://arxiv.org/abs/2301.07469


The length of the solar activity cycle fluctuates considerably. The temporal evolution of the corresponding cycle phase, that is, the deviation of the epochs of activity minima or maxima from strict periodicity, provides relevant information concerning the physical mechanism underlying the cyclic magnetic activity. An underlying strictly periodic process (akin to a perfect “clock”), with the observer seeing a superposition of the perfect clock and a small random phase perturbation, leads to long-term phase stability in the observations. Such behavior would be expected if cycles were synchronized by tides caused by orbiting planets or by a hypothetical torsional oscillation in the solar radiative interior. Alternatively, in the absence of such synchronization, phase fluctuations accumulate and a random walk of the phase ensues, which is a typical property of randomly perturbed dynamo models. Based on the sunspot record and the reconstruction of solar cycles from cosmogenic C14, we carried out rigorous statistical tests in order to decipher whether there exists phase synchronization or random walk. Synchronization is rejected at significance levels of between 95% (28 cycles from sunspot data) and beyond 99% (84 cycles reconstructed from C14, while the existence of random walk in the phases is consistent with all data sets. This result strongly supports randomly perturbed dynamo models with little inter-cycle memory.

Read this paper on arXiv…

E. Weisshaar, M. Schüssler and R. Cameron
Thu, 19 Jan 23
63/100

Comments: Astronomy & Astrophysics, in press

Transit timing variation analysis of the low-mass brown dwarf KELT-1 b [SSA]

Posted on by

http://arxiv.org/abs/2301.07619


We investigate whether there is a variation in the orbital period of the short-period brown dwarf-mass KELT-1\,b, which is one of the best candidates to observe orbital decay. We obtain 19 high-precision transit light curves of the target using six different telescopes. We add all precise and complete transit light curves from open databases and the literature, as well as the available TESS observations from sectors 17 and 57, to form a transit timing variation (TTV) diagram spanning more than 10 years of observations. The analysis of the TTV diagram, however, is inconclusive in terms of a secular or periodic variation, hinting that the system might have synchronized. We update the transit ephemeris and determine an informative lower limit for the reduced tidal quality parameter of its host star of Q$_{\star}^{\prime} > (8.5 \pm 3.9) \times 10^{6}$ assuming that the stellar rotation is not yet synchronised. Using our new photometric observations, published light curves, the TESS data, archival radial velocities and broadband magnitudes, we also update the measured parameters of the system. Our results are in good agreement with those found in previous analyses.

Read this paper on arXiv…

&. Baştürk, J. Southworth, S. Yalçınkaya, et. al.
Thu, 19 Jan 23
66/100

Comments: Accepted for publication by the MNRAS on 2023/01/16

Rossby waves on stellar equatorial beta-planes: uniformly rotating radiative stars [SSA]

Posted on by

http://arxiv.org/abs/2301.07446


Rossby waves arise due to the conservation of total vorticity in rotating fluids and may govern the large-scale dynamics of stellar interiors. Recent space missions collected huge information about the light curves and activity of many stars, which triggered observations of Rossby waves in stellar surface and interiors. We aim to study the theoretical properties of Rossby waves in stratified interiors of uniformly rotating radiative stars with sub-adiabatic vertical temperature gradient. We use the equatorial beta-plane approximation and linear vertical gradient of temperature to study the linear dynamics of equatorially trapped Rossby and inertia-gravity waves in interiors of radiative stars. The governing equation is solved by the method of separation of variables in the vertical and latitudinal directions. Vertical and latitudinal solutions of the waves are found to be governed by Bessel functions and Hermite polynomials, respectively. Appropriate boundary conditions at stellar surface and poles define analytical dispersion relations for Rossby, Rossby-gravity and inertia-gravity waves. The waves are confined in surface layers of 30-50 $H_0$, where $H_0$ is surface density scale height, and trapped between the latitudes of $\pm 60^0$. Observable frequencies (normalized by the angular frequency of the stellar rotation) of Rossby waves with $m=1$ ($m=2$), where $m$ is the toroidal wavenumber, are in the interval of 0.65-1 (1.4-2), depending on stellar rotation, radius and surface temperature. Rossby-type waves can be systematically observed using light curves of Kepler and TESS stars. Observations and theory then can be used for the sounding of stellar interiors.

Read this paper on arXiv…

M. Albekioni, T. Zaqarashvili and V. Kukhianidze
Thu, 19 Jan 23
70/100

Comments: N/A

Correcting Stellar Flare Frequency Distributions Detected by TESS and Kepler [SSA]

Posted on by

http://arxiv.org/abs/2301.07552


The habitability of planets is closely connected with the stellar activity, mainly the frequency of flares and the distribution of flare energy. Kepler and TESS find many flaring stars are detected via precise time-domain photometric data, and the frequency and energy distribution of stellar flares on different types of stars are studied statistically. However, the completeness and observational bias of detected flare events from different missions (e.g. Kepler and TESS) vary a lot. We use a unified data processing and detection method for flares events based on the light curve from Kepler and TESS. Then we perform injection and recovery tests in the original light curve of each star for each flare event to correct the completeness and energy of flares. Three samples of flaring stars are selected from Kepler and TESS, with rotating periods from 1 to $\sim$ 5 days. Adopting a hot-blackbody assumption, our results show that the cumulative flare frequency distributions (FFDs) of the same stars in Kepler and TESS bands tend to be consistent after correction, revealing a more natural flaring frequency and energy distribution. Our results also extend the low-energy limit in cumulative FFD fitting to $10^{31.5-33}$ erg on different types of stars. For solar-type stars, the average power-law index of cumulative FFD ($\alpha_{\rm cum}$) is $-0.84$, which indicates that low-energy flares contribute less to the total flare energy. With a piecewise correlation between $\alpha_{\rm cum}$ and $T_{\rm eff}$, $\alpha_{\rm cum}$ first rises with $T_{\rm eff}$ from M2 to K1 stars, then slightly decreases for stars hotter than K1.

Read this paper on arXiv…

D. Gao, H. Liu, M. Yang, et. al.
Thu, 19 Jan 23
71/100

Comments: 22 pages, 12 figures, 4 tables. Published in AJ

Identification of late-type stars of class I [SSA]

Posted on by

http://arxiv.org/abs/2301.07415


Aims. Gaia DR3 GSP-Phot and GSP-Spec parameters of known K- and M-type stars with luminosity class I are examined and compared with parameters collected from the literature, to assess their accuracy and their potential for stellar classification of unknown intrinsically bright late-types. Gaia DR3 GSP-Phot and GSP-Spec parameters were generated by the Astrophysical Parameters Inference Software (Apsis). Methods. In the Gaia DR3 catalog, there are about 40,000 entries with Apsis parameters similar to those of known red supergiants, RSGs, good parallaxes, and infrared 2MASS and WISE data. By using parallactic distances, infrared photometry, and variability information, only 203 new entries are found with luminosities and temperatures similar to that of known RSGs and G-band amplitudes smaller than 0.5 mag. Their low-resolution BP/RP spectra are compared with an empirically made spectral library of BP/RP spectra of known bright late-type stars (C-rich, S-type, O-rich asymptotic giant branch stars (AGBs), and RSGs) to obtain their spectral types. Results. Among them, 15 S-type stars are identified by peculiar absorption features due to ZrO and LaO visible in their BP/RP spectra, one S/C star, and nine C-rich stars by their strong CN absorption bands. K- and M-types can be reproduced with an accuracy of two subtypes. 20 new RSGs are confirmed, of which six have bolometric magnitudes brighter than those of the AGB limit: 2MASS J21015501+4517205, 2MASS J16291280-4956384, 2MASS J10192621-5818105, 2MASS J20230860+3651450, 2MASS J17084131-4026595, and 2MASS J16490055-4217328. The flag for C-rich stars of the Gaia DR3 LPV pipeline is erroneously true for some RSGs and a visual inspection of the BP/RP spectra is mandatory.

Read this paper on arXiv…

M. Messineo
Thu, 19 Jan 23
86/100

Comments: 17 figures, 18 pages, accepted by A&A

Explosive Events in the Quiet Sun Near and Beyond the Solar Limb Observed with the Interface Region Imaging Spectrograph (IRIS) [SSA]

Posted on by

http://arxiv.org/abs/2301.07190


We study point-like explosive events (EE), characterized by emission in the far wings of spectral lines, in a quiet region near the South Pole, using Interface Region Imaging Spectrograph (IRIS) spectra at two slit positions, slit-jaw (SJ) observations and Atmospheric Imaging Assembly (AIA) images. The events were best visible in SiIV spectra; they were weak in SJs, occasionally visible in 1600 A and 304 A AIA images, and invisible in higher temperature AIA images. We identified EEs from position–time images in the far wings of the SiIV lines and measured their distance from the limb. A Gaussian model of the height distribution showed that EEs occur in a narrow (0.9″) height range, centered at 3.2″ above the continuum limb at 2832.0 A. On the disk, we found that they occur in network boundaries. Further, we studied the line profiles of two bright EEs above the limb and one on the disk. We found that what appears as broad-band emission, is actually a superposition of 2–3 narrow-band Gaussian components with well-separated line profiles, indicating that material is expelled towards and/or away from the observer in discrete episodes in time and in space. The expelled plasma accelerates quickly, reaching line-of-sight (LOS) velocities up to 90 km/s. Overall, the motion was practically along the LOS, as the velocity on the plane of sky was small. In some cases tilted spectra were observed that could be interpreted in terms of rotating motions of up to 30 km/s. We did not find any strong absorption features in the wing of the SiIV lines, although in one case a very weak absorption feature was detected. No motions, indicative of jets, were detected in SJ or AIA images. Reconnection in an asymmetric magnetic-field geometry, in the middle or near the top of small loops is a plausible explanation of their observational characteristics.

Read this paper on arXiv…

C. Alissandrakis and J. Vial
Thu, 19 Jan 23
89/100

Comments: Accepted, Solar Physics

A Unified Model for Bipolar Outflows from Young Stars: Kinematic Signatures of Jets, Winds, and Their Magnetic Interplay with the Ambient Toroids [SSA]

Posted on by

http://arxiv.org/abs/2301.07447


Kinematic signatures of the jet, winds, multicavities, and episodic shells arising in the unified model of bipolar outflows developed in Shang et al.\ (2020), in which an outflow forms by radially directed, wide-angle toroidally magnetized winds interacting with magnetized isothermal toroids, are extracted in the form of position–velocity diagrams. Elongated outflow lobes, driven by magnetized winds and their interplay with the environment, are dominated by extended bubble structures with mixing layers beyond the conventional thin-shell models. The axial cylindrically stratified density jet carries a broad profile near the base, across the projected velocity of the wide-angle wind, and narrows down along the axis with the collimated flow. The reverse shock encloses the magnetized free wind, forms an innermost cavity, and deflects the flow pattern. Shear, Kelvin–Helmholtz instabilities, and pseudopulses add fine and distinctive features between the jet–shell components, and the fluctuating jet velocities. The broad webbed velocity features connect the extremely high and the low velocities across the multicavities, mimicking nested outflowing slower-wind components. Rings and ovals in the perpendicular cuts trace multicavities at different heights, and the compressed ambient gap regions enrich the low-velocity features with protruding spikes. Our kinematic signatures capture the observed systematics of the high-, intermediate-, and low-velocity components from Class 0 to II jet–outflow systems in molecular and atomic lines. The nested shells observed in HH 212, HH 30, and DG Tau B are naturally explained. Outflows as bubbles are ubiquitous and form an inevitable integrative outcome of the interaction between wind and ambient media.

Read this paper on arXiv…

H. Shang, C. Liu, R. Krasnopolsky, et. al.
Thu, 19 Jan 23
92/100

Comments: 66 pages, 26 figures, 3 tables, to appear in the Astrophysical Journal (2023)

Periodicities of solar activity and solar radiation derived from observations and their links with the terrestrial environment [SSA]

Posted on by

http://arxiv.org/abs/2301.07480


Solar magnetic activity is expressed via variations of sunspots and active regions varying on different timescales. The most accepted is an 11-year period supposedly induced by the electromagnetic solar dynamo mechanism. There are also some shorter or longer timescales detected: the biennial cycle (2-2.7 years), Gleisberg cycle (80-100 years), and Hallstatt’s cycle (2100-2300 years). Recently, using Principal Component Analysis (PCA) of the observed solar background magnetic field (SBMF), another period of 330-380 years, or Grand Solar Cycle (GSC), was derived from the summary curve of two eigenvectors of SBMF. In this paper, a spectral analysis of the averaged sunspot numbers, solar irradiance, and the summary curve of eigenvectors of SBMF was carried out using Morlet wavelet and Fourier transforms. We detect a 10.7-year cycle from the sunspots and modulus summary curve of eigenvectors as well a 22 years cycle and the grand solar cycle of 342-350-years from the summary curve of eigenvectors. The Gleissberg centennial cycle is only detected on the full set of averaged sunspot numbers for 400 years or by adding a quadruple component to the summary curve of eigenvectors. Another period of 2200-2300 years is detected in the Holocene data of solar irradiance measured from the abundance of $^{14}$C isotope. This period was also confirmed with the period of 2100 years derived from a baseline of the summary curve, supposedly, caused by the solar inertial motion (SIM) induced by the gravitation of large planets. The implication of these findings for different deposition of solar radiation into the northern and southern hemispheres of the Earth caused by the combined effects of the solar activity and solar inertial motion on the terrestrial atmosphere are also discussed.

Read this paper on arXiv…

V. Zharkova, I. Vasilieva, S. Shepherd, et. al.
Thu, 19 Jan 23
93/100

Comments: 30 pages, 15 figures

Massive pre-main-sequence stars in M17 — Modelling hydrogen and dust in MYSO disks [SSA]

Posted on by

http://arxiv.org/abs/2301.06819


The young massive-star-forming region M17 contains optically visible massive pre-main-sequence stars that are surrounded by circumstellar disks. Such disks are expected to disappear when these stars reach the main sequence. The physical and dynamical structure of these remnant disks are poorly constrained, especially the inner regions where accretion, photo-evaporation, and companion formation and migration may be ongoing. We aim to constrain the physical properties of the inner parts of the circumstellar disks of massive young stellar objects B243 (6 Msun) and B331 (12 Msun), two systems for which the central star has been detected and characterized previously despite strong dust extinction. Two-dimensional radiation thermo-chemical modelling with ProDiMo of double-peaked hydrogen lines of the Paschen and Brackett series observed with X-shooter was used to probe the properties of the inner disks. Additionally, the dust structure was studied by fitting the optical and near-infrared spectral energy distribution. B243 features a hot gaseous inner disk with dust at the sublimation radius at 3 AU. The disk appears truncated at roughly 6.5 AU; a cool outer disk of gas and dust may be present, but it cannot be detected with our data. B331 also has a hot gaseous inner disk. A gap separates the inner disk from a colder dusty outer disk starting at up to 100 AU. In both sources the inner disk extends to almost the stellar surface. Chemistry is essential for the ionization of hydrogen in these disks. The lack of a gap between the central objects and these disks suggests that they accrete through boundary-layer accretion. This would exclude the stars having a strong magnetic field. Their structures suggest that both disks are transitional in nature, that is to say they are in the process of being cleared, either through boundary-layer accretion, photo-evaporation, or through companion activity.

Read this paper on arXiv…

F. Backs, J. Poorta, C. Rab, et. al.
Wed, 18 Jan 23
17/133

Comments: 18 pages, 16 figures. Accepted for publication in A&A

Coronal Hole Analysis and Prediction using Computer Vision and LSTM Neural Network [SSA]

Posted on by

http://arxiv.org/abs/2301.06732


As humanity has begun to explore space, the significance of space weather has become apparent. It has been established that coronal holes, a type of space weather phenomenon, can impact the operation of aircraft and satellites. The coronal hole is an area on the sun characterized by open magnetic field lines and relatively low temperatures, which result in the emission of the solar wind at higher than average rates. In this study, To prepare for the impact of coronal holes on the Earth, we use computer vision to detect the coronal hole region and calculate its size based on images from the Solar Dynamics Observatory (SDO). We then implement deep learning techniques, specifically the Long Short-Term Memory (LSTM) method, to analyze trends in the coronal hole area data and predict its size for different sun regions over 7 days. By analyzing time series data on the coronal hole area, this study aims to identify patterns and trends in coronal hole behavior and understand how they may impact space weather events. This research represents an important step towards improving our ability to predict and prepare for space weather events that can affect Earth and technological systems.

Read this paper on arXiv…

J. Yun
Wed, 18 Jan 23
18/133

Comments: 15 pages

Speckle-interferometric study of close visual binary system Hip 11253 (HD14874) using Gaia (DR2) and (EDR3) [SSA]

Posted on by

http://arxiv.org/abs/2301.05968


We present a comprehensive set of physical and geometrical parameters for each of the components of the close visual binary system Hip 11253 (HD14874). We present an analysis for the binary and multiple stellar systems with the aim to obtain a match between the overall observational spectral energy distribution of the system and the spectral synthesis created from model atmospheres. The epoch positions are used to determine the orbital parameters and the total mass.

Read this paper on arXiv…

H. Aljboor and A. Taani
Wed, 18 Jan 23
31/133

Comments: Accepted for publication in RAA

Deciphering Faint Gyrosynchrotron Emission from Coronal Mass Ejection using Spectro-polarimetric Radio Imaging [SSA]

Posted on by

http://arxiv.org/abs/2301.06522


Measurements of the plasma parameters of coronal mass ejections (CMEs), particularly the magnetic field and non-thermal electron population entrained in the CME plasma, are crucial to understand their propagation, evolution, and geo-effectiveness. Spectral modeling of gyrosynchrotron (GS) emission from CME plasma has been regarded as one of the most promising remote sensing technique for estimating spatially resolved CME plasma parameters. Imaging the very low flux density CME GS emission in close proximity to the Sun with orders of magnitude higher flux density, however, has proven to be rather challenging. This challenge has only recently been met using the high dynamic range imaging capability of the Murchison Widefield Array (MWA). Although routine detection of GS is now within reach, the challenge has shifted to constraining the large number of free parameters in GS models, a few of which are degenerate, using the limited number of spectral points at which the observations are typically available. These degeneracies can be broken using polarimetric imaging. For the first time, we demonstrate this using our recently developed capability of high fidelity polarimetric imaging on the data from the MWA. We show that, in addition to breaking the degeneracies, spectro-polarimetric spectroscopic imaging also yields tighter constraints on the plasma parameters of key interest than possible with total intensity spectroscopic imaging alone.

Read this paper on arXiv…

D. Kansabanik, S. Mondal and D. Oberoi
Wed, 18 Jan 23
33/133

Comments: Submitted to the Astrophysical Journal, under review (21 pages, 15 figures, 2 tables)

Modelling the early mass-ejection in jet driven protostellar outflows. Lessons from Cep\,E [SSA]

Posted on by

http://arxiv.org/abs/2301.06146


We have used the axisymmetric chemo-hydrodynamical code WALKIMYA-2D to numerically model and reproduce the physical and CO emission properties of the jet-driven outflow from the intermediate-mass protostar Cep E, which was observed at $\sim 800$au resolution in the CO $J=2\to 1$ line with the IRAM interferometer. Our simulations take into account the observational constraints available on the physical structure of the protostellar envelope to provide constraints on the dynamics of the inner protostellar environment from the study of the outflow/jet propagation away from the launch region. WALKIMYA-2D successfully reproduces the main qualitative and quantitative features of the Cep E outflow and the jet kinematics, naturally accounting for their time variability. Signatures of internal shocks are detected as knots along the jet. In the early times of the ejection process, the young emitted knots interact with the dense circumstellar envelope through high-velocity, dissociative shocks, which strongly decrease the CO gas abundance in the jet. As time proceeds, the knots propagate more smoothly through the envelope and dissociative shocks disappear after $\sim 10^3$ yr. The distribution of CO abundance along the jet shows that the latter bears memory of the early dissociative phase in the course of its propagation. Analysis of the velocity field shows that the jet material mainly consists of gas entrained from the circumstellar envelope and accelerated away from the protostar at 700 au scale. As a result, the overall jet mass loss rate appears higher than the actual mass ejection rate by a factor $\sim 3$. Numerical modelling of the Cep E jet-driven outflow and comparison with the CO observations have allowed us to peer into the outflow formation mechanism with unprecedented detail and to retrieve the history of the mass-loss events that have shaped the outflow.

Read this paper on arXiv…

P. Rivera-Ortiz, A. Schutzer, B. Lefloch, et. al.
Wed, 18 Jan 23
37/133

Comments: N/A

Spectrophotometric analysis of magnetic white dwarf II: Helium-rich compositions [SSA]

Posted on by

http://arxiv.org/abs/2301.06605


We present an analysis of all single white dwarf stars known to exhibit spectroscopic signatures of neutral helium line splitting due to the presence of a strong magnetic field. Using state-of-the-art models taking into account the effects of magnetic fields on the synthetic spectra, we determine effective temperatures, surface gravities and masses for the stars in our sample. Our analysis uses data from the second and third Gaia (early) data release, photometric data from diverse surveys such as the Sloan Digital Sky Survey and Pan-STARRS, and archived spectroscopic data. We are able to successfully reproduce the spectra of 8 objects using an offset dipole geometry while several others seem to require either a more complexe geometry or a different chemical composition. We also highlight a group of hot featureless white dwarfs that are most probably highly magnetic objects whose spectra are completely smeared due to the field strength distribution across the surface.

Read this paper on arXiv…

F. Hardy, P. Dufour and S. Jordan
Wed, 18 Jan 23
41/133

Comments: 38 pages. Part 2 of 2. To be published in Monthly Notices of the Royal Astronomical Society

A neutron star candidate in the long-period binary 56 UMa [SSA]

Posted on by

http://arxiv.org/abs/2301.06531


56 UMa is a wide binary system containing a chemically peculiar red giant and a faint companion. Due to its surface chemical abundances, the red giant was classified as a Barium (Ba) star. This implies that the companion has to be a white dwarf, since Ba stars form when mass is transferred to them from an s-process rich Asymptotic Giant Branch (AGB) star. However, in the case of 56 UMa, the companion might be too massive to be the progeny of an AGB star that efficiently produced s-process elements like barium. In this letter, we revisit the orbital parameters of the system and perform a full spectral analysis with the goal of investigating the Ba-star classification of the giant and unravelling the nature of its faint companion. We combine radial-velocity and astrometric data to refine the orbital parameters of the system, including the orbital inclination and the companion mass. Then, we redetermine the stellar parameters of the giant and its chemical abundances using high-resolution HERMES spectra. Finally, we investigate the morphology of the interstellar gas in the vicinity of the system. The faint component in 56 UMa has a mass of $1.31 \pm 0.12$ M$_{\odot}$, which, together with the mixed s+r abundance profile of the red giant, confirms that the giant is not a standard Barium star. Additionally, the clear identification of a cavity surrounding 56 UMa could indicate that a supernova explosion occurred about 10$^5$ years ago in the system, suggesting that the faint companion might be a neutron star. However, finding an evolutionary scenario that explains all the observables is not trivial, so we discuss different possible configurations of the system and their respective merits.

Read this paper on arXiv…

A. Escorza, D. Karinkuzhi, A. Jorissen, et. al.
Wed, 18 Jan 23
50/133

Comments: Accepted for publication in A&AL

SDSS J134441.83+204408.3: A highly asynchronous, short-period magnetic cataclysmic variable with a 56 MG field strength [SSA]

Posted on by

http://arxiv.org/abs/2301.05723


When the accreting white dwarf in a magnetic cataclysmic variable star (mCV) has a field strength in excess of 10 MG, it is expected to synchronize its rotational frequency to the binary orbit frequency, particularly at small binary separations, due to the steep radial dependence of the magnetic field. We report the discovery of an mCV (SDSS J134441.83+204408.3; hereafter, J1344) that defies this expectation by displaying asynchronous rotation ($P_{spin}/P_{orb} = 0.893$) in spite of a high surface field strength (B=56 MG) and a short orbital period (114 min). Previously misidentified as a synchronously rotating mCV, J1344 was observed by TESS during sector 50, and the resulting power spectrum shows distinct spin and orbital frequencies, along with various sidebands and harmonics. Although there are several other asynchronous mCVs at short orbital periods, the presence of cyclotron humps in J1344’s SDSS spectrum makes it possible to directly measure the field strength in the cyclotron-emitting region; a previously study estimated 65 MG based on its identification of two cyclotron humps, but we revise this to 56$\pm$2 MG based on the detection of a third hump and on our modeling of the cyclotron spectrum. Short-period mCVs with field strengths above 10 MG are normally expected to be synchronous, so the highly asynchronous rotation in J1344 presents an interesting challenge for theoretical studies of spin-period evolution.

Read this paper on arXiv…

C. Littlefield, P. Mason, P. Garnavich, et. al.
Wed, 18 Jan 23
52/133

Comments: Accepted for publication in ApJL

gyre_tides: Modeling binary tides within the gyre stellar oscillation code [SSA]

Posted on by

http://arxiv.org/abs/2301.06599


We describe new functionality in the GYRE stellar oscillation code for modeling tides in binary systems. Using a multipolar expansion in space and a Fourier-series expansion in time, we decompose the tidal potential into a superposition of partial tidal potentials. The equations governing the small-amplitude response of a spherical star to an individual partial potential are the linear, non-radial, non-adiabatic oscillation equations with an extra inhomogeneous forcing term. We introduce a new executable, gyre_tides, that directly solves these equations within the GYRE numerical framework. Applying this to selected problems, we find general agreement with results in the published literature but also uncover some differences between our direct solution methodology and the modal decomposition approach adopted by many authors.
In its present form gyre_tides can model equilibrium and dynamical tides of aligned binaries in which radiative diffusion dominates the tidal dissipation (typically, intermediate and high-mass stars on the main sequence). Milestones for future development include incorporation of other dissipation processes, spin-orbit misalignment, and the Coriolis force arising from rotation.

Read this paper on arXiv…

M. Sun, R. Townsend and Z. Guo
Wed, 18 Jan 23
53/133

Comments: 15 pages, 8 figures, accepted for publication in ApJ; This new functionality, along with GYRE version 7.0, will be release in a few days from today (Jan 16th, 2013)

Center to limb variation of transition region Doppler shift in active regions [SSA]

Posted on by

http://arxiv.org/abs/2301.06723


Studying Doppler shifts provides deeper insights into the flow of mass and energy in the solar atmosphere. We perform a comprehensive measurement of Doppler shifts in the transition region and its center-to-limb variation (CLV) in the strong field regions ($|\textbf{B}| \geq$ 50 G) of 50 active regions (ARs), using the \ion{Si}{4} 1394~{\AA} line recorded by the Interface Region Imaging Spectrometer(IRIS). To locate the ARs and identify strong field regions, we have used the magnetograms obtained by the Helioseismic and Magnetic Imager (HMI). We find that in strong field regions, on average, all the ARs show mean redshifts ranging between 4{–}11~ km/s, which varies with ARs. These flows show a mild CLV, with sizable magnitudes at the limb and substantial scatter at the mid-longitude range. Our observations do not support the idea that redshifts in the lower transition region (T $<\sim$ 0.1 MK) are produced by field-aligned downflows as a result of impulsive heating and warrant alternative interpretation, such as downflow of type-\rm{II} spicules in the presence of a chromospheric wall created by cooler type-\rm{I} spicules.

Read this paper on arXiv…

A. Rajhans, D. Tripathi, V. Kashyap, et. al.
Wed, 18 Jan 23
68/133

Comments: Accepted for publication in the Astrophysical Journal on 16th January 2023

On the Generation and Evolution of Switchbacks and the Morphology of Alfvénic Transition: Low Mach-number Boundary Layers [SSA]

Posted on by

http://arxiv.org/abs/2301.05829


We investigate the generation and evolution of switchbacks (SBs), the nature of the sub-Alfv\’enic wind observed by Parker Solar Probe (PSP), and the morphology of the Alfv\’enic transition, all of which are key issues in solar wind research. First we highlight a special structure in the pristine solar wind, termed a low Mach-number boundary layer (LMBL). An increased Alfv\’en radius and suppressed SBs are observed within an LMBL. A probable source on the Sun for an LMBL is the peripheral region inside a coronal hole with rapidly diverging open fields. The sub-Alfv\’enic wind detected by PSP is an LMBL flow by nature. The similar origin and similar properties of the sub-Alfv\’enic intervals favor a wrinkled surface for the morphology of the Alfv\’enic transition. We find that a larger deflection angle tends to be associated with a higher Alfv\’en Mach number. The magnetic deflections have an origin well below the Alfv\’en critical point, and deflection angles larger than $90^{\circ}$ seem to occur only when $M_{\rm A} \gtrsim 2$. The velocity enhancement in units of the local Alfv\’en speed generally increases with the deflection angle, which is explained by a simple model. A nonlinearly evolved, saturated state is revealed for SBs, where the local Alfv\’en speed is roughly an upper bound for the velocity enhancement. In the context of these results, the most promising theory on the origin of SBs is the model of expanding waves and turbulence, and the patchy distribution of SBs is attributed to modulation by reductions in the Alfv\’en Mach number. Finally, a picture on the generation and evolution of SBs is created based on the results.

Read this paper on arXiv…

Y. Liu, H. Ran, H. Hu, et. al.
Wed, 18 Jan 23
78/133

Comments: 29 pages, 8 figures. Accepted for publication in The Astrophysical Journal

Probing Velocity Structures of Protostellar Envelopes: Infalling and Rotating Envelopes within Turbulent Dense Cores [SSA]

Posted on by

http://arxiv.org/abs/2301.06969


We have observed the three low-mass protostars, IRAS 15398$-$3359, L1527 IRS and TMC-1A, with the ALMA 12-m array, the ACA 7-m array, and the IRAM-30m and APEX telescopes in the C$^{18}$O $J=2$-1 emission. Overall, the C$^{18}$O emission shows clear velocity gradients at radii of $\sim$100-1000 au, which likely originate from rotation of envelopes, while velocity gradients are less clear and velocity structures are more perturbed on scales of $\sim$1000-10,000 au. IRAS 15398$-$3359 and L1527 IRS show a break at radii of $\sim$1200 and $\sim$1700 au in the radial profile of the peak velocity, respectively. The peak velocity is proportional to $r^{-1.38}$ or $r^{-1.7}$ within the break radius, which can be interpreted as indicating a rotational motion of the envelope with a degree of contamination of gas motions on larger spatial scales. The peak velocity follows $v_\mathrm{peak} \propto r^{0.68}$ or $v_\mathrm{peak} \propto r^{0.46}$ outside the break radius, which is similar to the $J/M$-$R$ relation of dense cores. TMC-1A exhibits the radial profile of the peak velocity not consistent with the rotational motion of the envelope nor the $J/M$-$R$ relation. The origin of the relation of $v_\mathrm{peak} \propto r^{0.46\operatorname{-}0.68}$ is investigated by examining correlations of the velocity deviation ($\delta v$) and the spatial scale ($\tau$) in the two sources. Obtained spatial correlations, $\delta v \propto \tau^{\sim0.6}$, are consistent with the scaling law predicted by turbulence models, which may suggest the large-scale velocity structures originate from turbulence.

Read this paper on arXiv…

J. Sai, N. Ohashi, H. Yen, et. al.
Wed, 18 Jan 23
83/133

Comments: 29 pages, 16 figures

Spectrophotometric analysis of magnetic white dwarf I: Hydrogen-rich compositions [SSA]

Posted on by

http://arxiv.org/abs/2301.06596


We present an homogeneous analysis of all DA stars labeled as magnetic in the Montreal White Dwarf Database (MWDD). Our sample is restricted to almost all known magnetic white dwarf showing clear sign of splitting ($B \gtrsim$ 1-2 MG) that have parallax measurements from the second Gaia data release, photometric data from diverse surveys and spectroscopic data from SDSS or archival data from the Montreal group. We determine the atmospheric parameters (effective temperature, surface gravity, magnetic field strength/geometry) of all objects using state-of-the-art model atmosphere/magnetic synthetic spectra, as well as reclassify many objects that were prematurely labeled as potentially magnetic. Finally, we discuss the atmospheric parameters/field properties distribution as well as the implication on our understanding of magnetic white dwarfs origin and evolution.

Read this paper on arXiv…

F. Hardy, P. Dufour and S. Jordan
Wed, 18 Jan 23
90/133

Comments: 140 pages. Part 1 of 2. To be published in Monthly Notices of the Royal Astronomical Society

Satellite observations of the Alfvénic Transition from Weak to Strong Magnetohydrodynamic Turbulence [SSA]

Posted on by

http://arxiv.org/abs/2301.06709


Plasma turbulence is a ubiquitous dynamical process that transfers energy across many spatial and temporal scales in astrophysical and space plasma systems. Although the theory of anisotropic magnetohydrodynamic (MHD) turbulence has successfully described phenomena in nature, its core prediction of an Alfvenic transition from weak to strong MHD turbulence when energy cascades from large to small scales has not been observationally confirmed. Here we report the first observational evidence for the Alfvenic weak-to-strong transition in MHD turbulence in the terrestrial magnetosheath using the four Cluster spacecraft. The observed transition indicates the universal existence of strong turbulence regardless of the initial level of MHD fluctuations. Moreover, the observations demonstrate that the nonlinear interactions of MHD turbulence play a crucial role in the energy cascade, widening the directions of the energy cascade and broadening the fluctuating frequencies. Our work takes a critical step toward understanding the complete picture of turbulence cascade, connecting the weak and strong MHD turbulence systems. It will have broad implications in star formation, energetic particle transport, turbulent dynamo, and solar corona or solar wind heating.

Read this paper on arXiv…

S. Zhao, H. Yan, T. Liu, et. al.
Wed, 18 Jan 23
93/133

Comments: submitted; 24 pages; 4 figures

Outburst Behaviour of the Dwarf Nova CG Draconis [SSA]

Posted on by

http://arxiv.org/abs/2301.05870


During the British Astronomical Association (BAA) 2022 campaign, 27436 photometric observations of the dwarf nova (DN) CG Draconis were made, with 106 eclipses recorded. This work summarizes the new data available and provides updated ephemeris and commentary on the observed eclipse profiles. The orbital period found is P_orb = 4h31m38s +/- 1s. Two types of quasi-periodic outbursts are identified: normal outbursts, of Delta V of approximately 1.25 mag amplitude, and bright, of Delta V of approximately 1.5 mag. The pattern resembles superoutbursts of SU UMa-type DNe, however, no presence of superhumps characterizing these DNe was found. Given CG Dra is located above the period gap, it may represent a new intermediary subtype between SS Cyg and SU UMa-type stars, or provide support to superoutburst models that do not rely on eccentric accretion disks.

Read this paper on arXiv…

M. Usatov and J. Shears
Wed, 18 Jan 23
94/133

Comments: Accepted for publication in Astronomische Nachrichten

Computing the gravitational potential on nested meshes using the convolution method [SSA]

Posted on by

http://arxiv.org/abs/2301.06763


Aims. Our aim is to derive a fast and accurate method for computing the gravitational potential of astrophysical objects with high contrasts in density, for which nested or adaptive meshes are required. Methods. We present an extension of the convolution method for computing the gravitational potential to the nested Cartesian grids. The method makes use of the convolution theorem to compute the gravitational potential using its integral form. Results. A comparison of our method with the iterative outside-in conjugate gradient and generalized minimal residual methods for solving the Poisson equation using nonspherically symmetric density configurations has shown a comparable performance in terms of the errors relative to the analytic solutions. However, the convolution method is characterized by several advantages and outperforms the considered iterative methods by factors 10–200 in terms of the runtime, especially when graphics processor units are utilized. The convolution method also shows an overall second-order convergence, except for the errors at the grid interfaces where the convergence is linear. Conclusions. High computational speed and ease in implementation can make the convolution method a preferred choice when using a large number of nested grids. The convolution method, however, becomes more computationally costly if the dipole moments of tightly spaced gravitating objects are to be considered at coarser grids.

Read this paper on arXiv…

E. Vorobyov, J. McKevitt, I. Kulikov, et. al.
Wed, 18 Jan 23
97/133

Comments: Accepted for publication in Astronomy & Astrophysics

The nebula around the binary post-AGB star 89 Herculis [SSA]

Posted on by

http://arxiv.org/abs/2301.06965


There is a class of binary post-asymptotic giant branch (post-AGB) stars that exhibit remarkable near-infrared (NIR) excess. These stars are surrounded by disks with Keplerian or quasi-Keplerian dynamics and outflows composed of gas escaping from the rotating disk. Depending on the dominance of these components, there are two subclasses of binary post-AGB stars: disk-dominated and outflow-dominated. We aim to properly study the hourglass-like structure that surrounds the Keplerian disk around 89 Her. We present total-power on-the-fly maps of $^{12}$CO and $^{13}$CO $J$=2-1 emission lines in 89 Her. Previous studies are known to suffer from flux losses in the most extended components. We merge these total-power maps with previous NOEMA maps. The resulting combined maps are expected to detect the whole nebula extent of the source. Our new combined maps contain the entirety of the detectable flux of the source and at the same time are of high spatial resolution thanks to the interferometric observations. We find that the hourglass-like extended outflow around the rotating disk is larger and more massive than suggested by previous works. The total nebular mass of this very extended nebula is 1.8E-2 solar masses, of which 65% comes from the outflow. The observational data and model results lead us to classify the envelope around 89 Her as an outflow-dominated nebula, together with R Sct and IRAS 19125+0343 (and very probably AI CMi, IRAS 20056+1834, and IRAS 18123+0511). The updated statistics on the masses of the two post-AGB main components reveal that there are two distinct subclasses of nebulae around binary post-AGB stars depending on which component is the dominant one. We speculate that the absence of an intermediate subclass of sources is due to the different initial conditions of the stellar system and not because both subclasses are in different stages of the post-AGB evolution.

Read this paper on arXiv…

I. Cava, J. Alcolea, V. Bujarrabal, et. al.
Wed, 18 Jan 23
100/133

Comments: Accepted 5 January 2023 in Astronomy & Astrophysics. 17 pages

The SOUL view of IRAS20126+4104. Kinematics and variability of the H$_2$ jet from a massive protostar [SSA]

Posted on by

http://arxiv.org/abs/2301.06832


We exploit the increased sensitivity of the recently installed AO SOUL at the LBT to obtain new high-spatial-resolution NIR images of the massive young stellar object IRAS20126+4104 and its outflow. We aim to derive the jet proper motions and kinematics, as well as to study its photometric variability by combining the novel performances of SOUL together with previous NIR images. We used both broad-band ($K_{s}$, $K’$) and narrow-band (Br$\gamma$, H2) observations from a number of NIR cameras (UKIRT/UFTI,SUBARU/CIAO,TNG/NICS,LBT/PISCES,and LBT/LUCI1) to derive maps of the continuum and the H$_2$ emission in the 2.12 $\mu$m line. Three sets of images, obtained with AO systems (CIAO,2003; FLAO,2012; SOUL,2020), allowed us to derive the proper motions of a large number of H$_2$ knots along the jet. Photometry from all images was used to study the jet variability. We derived knot proper motions in the range of 1.7-20.3 mas yr$^{-1}$ (i.e. 13-158 km s$^{-1}$ at 1.64 kpc, avg. outflow tangential velocity $\sim$ 80 km s$^{-1}$). The derived knot dynamical age spans a $\sim$ 200-4000 yr interval. A ring-like H$_2$ feature near the protostar location exhibits peculiar kinematics and may represent the outcome of a wide-angle wind impinging on the outflow cavity. Both H$_2$ geometry and velocities agree with those inferred from proper motions of the H$_2$O masers, located at a smaller distance from the protostar. Although the total H$_2$ line emission from the knots does not exhibit time variations at a $\widetilde{>}$ 0.3 mag level, we have found a clear continuum flux variation (radiation scattered by the dust in the cavity opened by the jet) which is anti-correlated between the blue-shifted and red-shifted lobes and may be periodic (with a period of $\sim$ 12-18 yr). We suggest that the continuum variability might be related to inner-disc oscillations which have also caused the jet precession.

Read this paper on arXiv…

F. Massi, A. Garatti, R. Cesaroni, et. al.
Wed, 18 Jan 23
110/133

Comments: 26 pages, 22 figures, 2 mpeg files, accepted by Astronomy & Astrophysics

Optical characterization and Radial velocity monitoring with Belgian and Indian Telescopes (ORBIT): the eclipsing binaries EPIC 211982753 and EPIC 211915147 [SSA]

Posted on by

http://arxiv.org/abs/2301.06125


The K2 eclipsing binary candidates EPIC 211982753 (hereinafter called EPIC2753) and EPIC 211915147 (hereinafter called EPIC5147) are characterized with the help of photometric and high-resolution spectroscopic data. The light curve analysis uses the R-band photometric data from the 1.3-m Devasthal Fast Optical Telescope (DFOT, India), ASAS-3 and K2 observations. High-resolution echelle spectra are collected using the HERMES spectrograph at the 1.2-m MERCATOR telescope (La Palma, Spain). The synthetic light and radial velocity curves are generated with the help of the modeling package PHOEBE 1.0. The orbital period analysis based on the ~3.2 years of K2 observations does not show any change in the orbital period of both targets. The component masses M1,2 are estimated as 1.69(0.02) and 1.59(0.02) solar mass for EPIC2753, and 1.48(0.01) and 1.27(0.01) solar mass for EPIC5147. Both systems are high mass-ratio eclipsing binaries with q>0.85. The component radii R1,2 are found to be 1.66(0.02) and 1.53(0.02) solar radius for EPIC2753, and 1.80(0.05) and 1.42(0.05) solar radius for EPIC5147. The distances of EPIC2753 and EPIC5147 are determined as 238(4) and 199(5) pc, respectively. MESA Isochrones and Stellar Tracks are used to understand the evolutionary status of both systems.

Read this paper on arXiv…

A. Panchal, Y. Joshi, P. Cat, et. al.
Wed, 18 Jan 23
116/133

Comments: Submitted for publication

Discovery of the Exceptionally Short Period Ultracool Dwarf Binary LP 413-53AB [SSA]

Posted on by

http://arxiv.org/abs/2301.07039


We report the detection of large-amplitude, rapid radial velocity (RV) variations and line-splitting in high-resolution Keck/NIRSPEC spectra of the M9 dwarf LP 413-53. We attribute these features to binary motion. Analyzing data spanning 9 months, we infer an orbital period of 0.852725$^{+0.000002}{-0.000003}$~day, an eccentricity of 0.080$^{+0.020}{-0.013}$, a primary RV semi-amplitude of 24.2$^{+1.8}{-1.4}$ km~s$^{-1}$, and a secondary RV semi-amplitude of 29.4$^{+2.2}{-1.7}$ km~s$^{-1}$, implying a system mass ratio $M_\mathrm{secondary}$/$M_\mathrm{primary}$ = 0.822$^{+0.009}_{-0.008}$. These measurements identify LP 413-53 as the shortest-period ultracool binary discovered to date, and one of the smallest separation main sequence binaries known. The position and velocity of the system rules out previously reported membership in the Hyades Moving Group, and indicate that this is likely a pair of evolved (age $\gtrsim$ 1 Gyr), very-low-mass stars. Assuming masses consistent with evolved late-M and L dwarfs, we estimate an orbital separation of 0.0093-0.0095~au or 19-22 stellar radii, and an orbital inclination angle of 27$\pm$2 deg, making it unlikely that this system exhibits eclipse events. The larger radii of these stars at young ages would have put them in contact at the system’s current separation, and we speculate that this system has undergone dynamical evolution, either through orbital angular momentum loss or ejection of a third component followed by tidal circularization.

Read this paper on arXiv…

C. Hsu, A. Burgasser and C. Theissen
Wed, 18 Jan 23
125/133

Comments: 13 pages, 3 figures. Submitted to ApJ Letters; comments welcome

Mass outflow from the symbiotic binary RS Oph during its 2021 outburst [SSA]

Posted on by

http://arxiv.org/abs/2301.06643


RS Oph is a symbiotic recurrent nova containing a massive white dwarf with heavy mass loss during activity. In August 2021, it underwent its seventh optical eruption since the end of the 19th century. The goal of this work is to analyse the structure of the outflows from the outbursting object. Based on broad-band $U$, $B$, $V$, $R_{\rm C}$, and $I_{\rm C}$ photometry and high-resolution H$\alpha$ spectroscopy obtained at days 11–15 of the outburst, we derived some parameters of the system’s components and outflows and their changes during our observation. The effective temperature of a warm shell (pseudophotosphere) produced by the ejected material and occulting the hot component of the system was $T_{eff}=15000\pm1000$ K and the electron temperature of the nebula was $T_{e}=17000\pm3000$ K throughout the observations. The effective radius of the pseudophotosphere was $R_{ eff}=13.3\pm2.0$ R${\odot}$ and the emission measure of the nebula $EM=(9.50\pm0.59) $10$^{61}$ cm$^{-3}$ for day 11 and $R{eff}=10.3\pm1.6$ R${\odot}$ and $EM=(5.60\pm0.35)$10$^{61}$ cm$^{-3}$ for day 15. To provide this emission measure, the bolometric luminosity of the outbursting object must exceed its Eddington limit. The mass-loss rate of the outbursting object through its wind is much greater than through its streams. The total rate (from wind + streams) was less than $(4-5)$ 10$^{-5}$ (d/1.6kpc)$^{3/2}$ M${\odot}$yr$^{-1}$. The streams are not highly collimated. Their mean outflowing velocities are $\upsilon_{b}=-3680\pm60$ km s$^{-1}$ for the approaching stream and $\upsilon_{r}=3520\pm50$ km s$^{-1}$ for the receding one if the orbit inclination is 50$^\circ$.

Read this paper on arXiv…

N. Tomov, M. Tomova, K. Stoyanov, et. al.
Wed, 18 Jan 23
131/133

Comments: 8 pages, 2 figures; accepted in Astronomy & Astrophysics

Exploring magnetic loops and serpentine fields in the quiet Sun with the GRIS-IFU [SSA]

Posted on by

http://arxiv.org/abs/2301.05591


Synthetic observations produced from radiative magnetohydronamic simulations have predicted that higher polarization fractions in the quiet solar photosphere would be revealed by increasing the total integration time of observations at GREGOR resolutions. We present recently acquired disk centre observations of the Fe I $15648.5$ $\mathrm{\AA}$ line obtained with the GREGOR telescope equipped with the GRIS-IFU during excellent seeing conditions, showing exceptionally high polarization fractions. Our observation reveal an internetwork region with a majority ($>60\%$) of magnetised pixels displaying a clear transverse component of the magnetic field. This result is in stark contrast to previous disk-centre GRIS-IFU observations in this spectral line, which had predominantly vertical magnetic fields in the deep photosphere. At the same time, the median magnetic field strength is weaker than previous GRIS-IFU observations, indicating that the larger fraction of polarization signals cannot be explained by a more active target. We use the Stokes Inversion based on Response functions (SIR) code to analyse the data, performing over $45$ million inversions, and interrogate the impact of two conflicting approaches to the treatment of noise on the retrieval of the magnetic inclination and azimuth. We present several case studies of the zoo of magnetic features present in these data, including small-scale magnetic loops that seem to be embedded in a sea of magnetism, and serpentine fields, focusing on regions where full-vector spectropolarimetry has been achieved. We also present a new open-source Python 3 analysis tool, SIR Explorer (SIRE), that we use to examine the dynamics of these small-scale magnetic features.

Read this paper on arXiv…

R. Campbell, R. Gafeira, M. Mathioudakis, et. al.
Mon, 16 Jan 23
8/50

Comments: 17 pages, 11 figures, Accepted for publication in ApJ

First Perihelion of EUI on the Solar Orbiter mission [SSA]

Posted on by

http://arxiv.org/abs/2301.05616


Context. The Extreme Ultraviolet Imager (EUI), onboard Solar Orbiter consists of three telescopes: the two High Resolution Imagers in EUV (HRIEUV) and in Lyman-{\alpha} (HRILya), and the Full Sun Imager (FSI). Solar Orbiter/EUI started its Nominal Mission Phase on 2021 November 27. Aims. EUI images from the largest scales in the extended corona off limb, down to the smallest features at the base of the corona and chromosphere. EUI is therefore a key instrument for the connection science that is at the heart of the Solar Orbiter mission science goals. Methods. The highest resolution on the Sun is achieved when Solar Orbiter passes through the perihelion part of its orbit. On 2022 March 26, Solar Orbiter reached for the first time a distance to the Sun close to 0.3 au. No other coronal EUV imager has been this close to the Sun. Results. We review the EUI data sets obtained during the period 2022 March-April, when Solar Orbiter quickly moved from alignment with the Earth (2022 March 6), to perihelion (2022 March 26), to quadrature with the Earth (2022 March 29). We highlight the first observational results in these unique data sets and we report on the in-flight instrument performance. Conclusions. EUI has obtained the highest resolution images ever of the solar corona in the quiet Sun and polar coronal holes. Several active regions were imaged at unprecedented cadences and sequence durations. We identify in this paper a broad range of features that require deeper studies. Both FSI and HRIEUV operate at design specifications but HRILya suffered from performance issues near perihelion. We conclude emphasising the EUI open data policy and encouraging further detailed analysis of the events highlighted in this paper.

Read this paper on arXiv…

D. Berghmans, P. Antolin, F. Auchère, et. al.
Mon, 16 Jan 23
9/50

Comments: N/A

Surface magnetic field of the A-type metallic-line star omicron Pegasi revisited [SSA]

Posted on by

http://arxiv.org/abs/2301.05367


The bright A-type metallic-line star o Peg was reported in the early 1990s to have a surface magnetic field of ~2kG by analyzing the widths and strengths of spectral lines. In respect that those old studies were of rather empirical or approximate nature and the quality of observational data was not sufficient, this problem has been newly reinvestigated based on physically more rigorous simulations of line flux profiles, along with the observed equivalent widths (W) and full-widths at half-maximum (h) of 198 Fe I and 182 Fe II lines measured from the high-quality spectra. Given the Fe abundance derived from the conventional analysis, theoretical W and h values calculated for various sets of parameters were compared with the observed ones, which lead to the following conclusion regarding <H> (mean field strength). (1) An analysis of W yielded <H>~1-1.5kG from Fe II lines with the microturbulence of vt~1.5km/s. (2) A comparison of h resulted in <H>~1.5-2kG as well as the projected rotational velocity of vsini~5km/s. (3) Accordingly, the existence of mean magnetic field on the order of <H>~1-2kG in o Peg was confirmed, which is almost consistent with the consequence of the previous work.

Read this paper on arXiv…

Y. Takeda
Mon, 16 Jan 23
15/50

Comments: 17 pages including 10 figures and 4 tables (with supplementary materials); accepted for publication in Astronomishe Nachrichten

HST Low Resolution Stellar Library [SSA]

Posted on by

http://arxiv.org/abs/2301.05335


Hubble Space Telescope’s (HST) Space Telescope Imaging Spectrograph (STIS) targeted 556 stars in a long-running program called Next Generation Spectral Library (NGSL) via proposals GO9088, GO9786, GO10222, and GO13776. Exposures through three low resolution gratings provide wavelength coverage from 0.2 $< \lambda <$ 1 $\mu$m at $\lambda/\Delta\lambda\sim$ 1000, providing unique coverage in the ultraviolet (UV). The UV grating (G230LB) scatters red light and this results in unwanted flux that becomes especially troubling for cool stars. We applied scattered light corrections based on \cite{2022stis.rept….5W} and flux corrections arising from pointing errors relative to the center of the 0\farcs2 slit. We present 514 fully reduced spectra, fluxed, dereddened, and cross-correlated to zero velocity. Because of the broad spectral range, we can simultaneously study H$\alpha$ and Mg II $\lambda$2800, indicators of chromospheric activity. Their behaviours are decoupled. Besides three cool dwarfs and one giant with mild flares in H$\alpha$, only Be stars show strong H$\alpha$ emission. Mg2800 emission, however, strongly anti-correlates with temperature such that warm stars show absorption and stars cooler than $5000 : ! \rm{K}$ universally show chromospheric emission regardless of dwarf/giant status or metallicity. Transformed to Mg2800 flux emerging from the stellar surface, we find a correlation with temperature with approximately symmetric astrophysical scatter, in contrast to other workers who find a basal level with asymmetric scatter to strong values. Unsurprisingly, we confirm that Mg2800 activity is variable.

Read this paper on arXiv…

T. Pal, I. Khan, G. Worthey, et. al.
Mon, 16 Jan 23
25/50

Comments: 18 pages, 18 figures, 3 tables. Full version of table 3 is available online

Interpretation of flat energy spectra upstream of fast interplanetary shocks [SSA]

Posted on by

http://arxiv.org/abs/2301.05454


Interplanetary shocks are large-scale heliospheric structures often caused by eruptive phenomena at the Sun, and represent one of the main sources of energetic particles. Several interplanetary shock crossings by spacecraft at $1$ AU have revealed enhanced energetic-ion fluxes that extend far upstream of the shock. Surprisingly, in some shock events, ion fluxes with energies between $100$ keV and about $2$ MeV acquire similar values (which we refer to as “overlapped” fluxes), corresponding to flat energy spectra in that range. In contrast, closer to the shock, the fluxes are observed to depend on energy. In this work, we analyze three interplanetary shock-related energetic particle events observed by the Advanced Composition Explorer spacecraft where flat ion energy spectra were observed upstream of the shock. We interpret these observations via a velocity filter mechanism for particles in a given energy range. This reveals that low energy particles tend to be confined to the shock front and cannot easily propagate upstream, while high energy particles can. The velocity filter mechanism has been corroborated from observations of particle flux anisotropy by the Solid-State Telescope of Wind/3DP.

Read this paper on arXiv…

S. Perri, G. Prete, G. Zimbardo, et. al.
Mon, 16 Jan 23
27/50

Comments: N/A

A photometric study of NSVS 7453183: a probable quadruple system with long-term surface activity [SSA]

Posted on by

http://arxiv.org/abs/2301.05617


The $VRC$ light curves were regularly measured for the eclipsing binary NSVS 7453183 as a part of our long-term observational project for studying of low-mass eclipsing binaries with a short orbital period and surface activity. The TESS light curve solution in Phoebe results to the detached configuration, where the temperature of primary component was adopted to $T_1$ = 4300 K according to the SED approximation. It gives us $T_2 =$ 4080 $\pm$ 100 K for the secondary component. The spectral type of the primary component was estimated to be K6 and the photometric mass ratio was derived $q = 0.86$. We confirm presence of the third body in this system, a stellar companion with a minimal mass 0.33 M${\rm Sun}$ orbiting the eclipsing pair with a short period about 425 days, and propose the next, fourth body with a longer orbiting period of about 12 years, probably a brown dwarf with the minimal mass of 50 M${\rm Jup}$. The hierarchical structure ((1+1)+1)+1 of this quadruple system is assumed. Characteristics and temporal variations of the dark region on the surface of the primary component were estimated. The average migration speed of about 10 deg/month was found during years 2020-2022.

Read this paper on arXiv…

L. Šmelcer, M. Wolf, H. Kučáková, et. al.
Mon, 16 Jan 23
38/50

Comments: Accepted for publication in MNRAS. 11 pages, 9 figures, 9 tables. This is the authors’ version of the accepted manuscript

Excitation of Multi-periodic Kink Motions in Solar Flare Loops: Possible Application to Quasi-periodic Pulsations [SSA]

Posted on by

http://arxiv.org/abs/2301.05382


Magnetohydrodynamic (MHD) waves are often invoked to interpret quasi-periodic pulsations (QPPs) in solar flares. We study the response of a straight flare loop to a kink-like velocity perturbation using three-dimensional MHD simulations and forward model the microwave emissions using the fast gyrosynchrotron code. Kink motions with two periodicities are simultaneously generated,with the long-period component P_L = 57s being attributed to the radial fundamental kink mode and the short-period component P_S=5.8s to the first leaky kink mode. Forward modeling results show that the two-periodic oscillations are detectable in the microwave intensities for some lines of sight. Increasing the beam size to (1″)^2 does not wipe out the microwave oscillations. We propose that the first leaky kink mode is a promising candidate mechanism to account for short-period QPPs. Radio telescopes with high spatial resolutions can help distinguish between this new mechanism with such customary interpretations as sausage modes.

Read this paper on arXiv…

M. Shi, B. Li, S. Chen, et. al.
Mon, 16 Jan 23
39/50

Comments: Accepted for publication in ApJL

A synchronized two-dimensional $α-Ω$ model of the solar dynamo [SSA]

Posted on by

http://arxiv.org/abs/2301.05452


We consider a conventional $\alpha-\Omega$-dynamo model with meridional circulation that exhibits typical features of the solar dynamo, including a Hale cycle period of around 20 years and a reasonable shape of the butterfly diagram. With regard to recent ideas of a tidal synchronization of the solar cycle, we complement this model by an additional time-periodic $\alpha$-term that is localized in the tachocline region. It is shown that amplitudes of some dm/s are sufficient for this $\alpha$-term to become capable of entraining the underlying dynamo. We argue that such amplitudes of $\alpha$ may indeed be realistic, since velocities in the range of m/s are reachable, e.g., for tidally excited magneto-Rossby waves.

Read this paper on arXiv…

M. Klevs, F. Stefani and L. Jouve
Mon, 16 Jan 23
42/50

Comments: 14 pages, 6 figures

On the Role of Interplanetary Shocks in Accelerating MeV Electrons [SSA]

Posted on by

http://arxiv.org/abs/2301.05587


One of the sources of solar energetic particle (SEP) events is shocks that are driven by fast coronal mass ejections (CMEs). They can accelerate SEPs up to relativistic energies and are attributed to the largest SEP events. New studies suggest that CME-driven shocks can potentially accelerate electrons to MeV energies in the vicinity of the Sun. We focus on relativistic electrons associated with strong IP shocks between 2007 and 2019 to determine whether the shocks can keep accelerating such electrons up to 1 AU distance. We have analyzed High Energy Telescope (HET) observations aboard the STEREO spacecraft of potential electron energetic storm particle (ESP) events, characterized by intensity time series that peak at the time of, or close to, the associated CME-driven shock crossing. We present a new filtering method to assess the statistical significance of particle intensity increases and apply it to MeV electron observations in the vicinity of interplanetary shocks. We identified 27 candidate events by visual inspection from a STEREO in-situ shock list. Our method identified nine clear cases, where a significant increase of MeV electrons was found in association with a shock. Typically, the highest statistical significance was observed in the highest HET energy channel of electrons. All nine cases were associated with shocks driven by interplanetary CMEs that showed large transit speeds, in excess of 900 km/s. In several cases multiple shocks were observed within one day of the shock related to the electron increase. Although electron ESP events at MeV energies are found to be rare at 1 AU our filtering method is not designed to identify a potential interplanetary shock contribution from distances closer to the Sun. Future observations taken during closer approaches to the Sun will likely provide clarity on interplanetary shock acceleration of electrons.

Read this paper on arXiv…

N. Sheshvan, N. Dresing, R. Vainio, et. al.
Mon, 16 Jan 23
49/50

Comments: 13 pages, submitted to A&A

Exploring magnetic loops and serpentine fields in the quiet Sun with the GRIS-IFU [SSA]

Posted on by

http://arxiv.org/abs/2301.05591


Synthetic observations produced from radiative magnetohydronamic simulations have predicted that higher polarization fractions in the quiet solar photosphere would be revealed by increasing the total integration time of observations at GREGOR resolutions. We present recently acquired disk centre observations of the Fe I $15648.5$ $\mathrm{\AA}$ line obtained with the GREGOR telescope equipped with the GRIS-IFU during excellent seeing conditions, showing exceptionally high polarization fractions. Our observation reveal an internetwork region with a majority ($>60\%$) of magnetised pixels displaying a clear transverse component of the magnetic field. This result is in stark contrast to previous disk-centre GRIS-IFU observations in this spectral line, which had predominantly vertical magnetic fields in the deep photosphere. At the same time, the median magnetic field strength is weaker than previous GRIS-IFU observations, indicating that the larger fraction of polarization signals cannot be explained by a more active target. We use the Stokes Inversion based on Response functions (SIR) code to analyse the data, performing over $45$ million inversions, and interrogate the impact of two conflicting approaches to the treatment of noise on the retrieval of the magnetic inclination and azimuth. We present several case studies of the zoo of magnetic features present in these data, including small-scale magnetic loops that seem to be embedded in a sea of magnetism, and serpentine fields, focusing on regions where full-vector spectropolarimetry has been achieved. We also present a new open-source Python 3 analysis tool, SIR Explorer (SIRE), that we use to examine the dynamics of these small-scale magnetic features.

Read this paper on arXiv…

R. Campbell, R. Gafeira, M. Mathioudakis, et. al.
Mon, 16 Jan 23
10/50

Comments: 17 pages, 11 figures, Accepted for publication in ApJ

First Perihelion of EUI on the Solar Orbiter mission [SSA]

Posted on by

http://arxiv.org/abs/2301.05616


Context. The Extreme Ultraviolet Imager (EUI), onboard Solar Orbiter consists of three telescopes: the two High Resolution Imagers in EUV (HRIEUV) and in Lyman-{\alpha} (HRILya), and the Full Sun Imager (FSI). Solar Orbiter/EUI started its Nominal Mission Phase on 2021 November 27. Aims. EUI images from the largest scales in the extended corona off limb, down to the smallest features at the base of the corona and chromosphere. EUI is therefore a key instrument for the connection science that is at the heart of the Solar Orbiter mission science goals. Methods. The highest resolution on the Sun is achieved when Solar Orbiter passes through the perihelion part of its orbit. On 2022 March 26, Solar Orbiter reached for the first time a distance to the Sun close to 0.3 au. No other coronal EUV imager has been this close to the Sun. Results. We review the EUI data sets obtained during the period 2022 March-April, when Solar Orbiter quickly moved from alignment with the Earth (2022 March 6), to perihelion (2022 March 26), to quadrature with the Earth (2022 March 29). We highlight the first observational results in these unique data sets and we report on the in-flight instrument performance. Conclusions. EUI has obtained the highest resolution images ever of the solar corona in the quiet Sun and polar coronal holes. Several active regions were imaged at unprecedented cadences and sequence durations. We identify in this paper a broad range of features that require deeper studies. Both FSI and HRIEUV operate at design specifications but HRILya suffered from performance issues near perihelion. We conclude emphasising the EUI open data policy and encouraging further detailed analysis of the events highlighted in this paper.

Read this paper on arXiv…

D. Berghmans, P. Antolin, F. Auchère, et. al.
Mon, 16 Jan 23
16/50

Comments: N/A

A synchronized two-dimensional $α-Ω$ model of the solar dynamo [SSA]

Posted on by

http://arxiv.org/abs/2301.05452


We consider a conventional $\alpha-\Omega$-dynamo model with meridional circulation that exhibits typical features of the solar dynamo, including a Hale cycle period of around 20 years and a reasonable shape of the butterfly diagram. With regard to recent ideas of a tidal synchronization of the solar cycle, we complement this model by an additional time-periodic $\alpha$-term that is localized in the tachocline region. It is shown that amplitudes of some dm/s are sufficient for this $\alpha$-term to become capable of entraining the underlying dynamo. We argue that such amplitudes of $\alpha$ may indeed be realistic, since velocities in the range of m/s are reachable, e.g., for tidally excited magneto-Rossby waves.

Read this paper on arXiv…

M. Klevs, F. Stefani and L. Jouve
Mon, 16 Jan 23
21/50

Comments: 14 pages, 6 figures

Excitation of Multi-periodic Kink Motions in Solar Flare Loops: Possible Application to Quasi-periodic Pulsations [SSA]

Posted on by

http://arxiv.org/abs/2301.05382


Magnetohydrodynamic (MHD) waves are often invoked to interpret quasi-periodic pulsations (QPPs) in solar flares. We study the response of a straight flare loop to a kink-like velocity perturbation using three-dimensional MHD simulations and forward model the microwave emissions using the fast gyrosynchrotron code. Kink motions with two periodicities are simultaneously generated,with the long-period component P_L = 57s being attributed to the radial fundamental kink mode and the short-period component P_S=5.8s to the first leaky kink mode. Forward modeling results show that the two-periodic oscillations are detectable in the microwave intensities for some lines of sight. Increasing the beam size to (1″)^2 does not wipe out the microwave oscillations. We propose that the first leaky kink mode is a promising candidate mechanism to account for short-period QPPs. Radio telescopes with high spatial resolutions can help distinguish between this new mechanism with such customary interpretations as sausage modes.

Read this paper on arXiv…

M. Shi, B. Li, S. Chen, et. al.
Mon, 16 Jan 23
28/50

Comments: Accepted for publication in ApJL

Interpretation of flat energy spectra upstream of fast interplanetary shocks [SSA]

Posted on by

http://arxiv.org/abs/2301.05454


Interplanetary shocks are large-scale heliospheric structures often caused by eruptive phenomena at the Sun, and represent one of the main sources of energetic particles. Several interplanetary shock crossings by spacecraft at $1$ AU have revealed enhanced energetic-ion fluxes that extend far upstream of the shock. Surprisingly, in some shock events, ion fluxes with energies between $100$ keV and about $2$ MeV acquire similar values (which we refer to as “overlapped” fluxes), corresponding to flat energy spectra in that range. In contrast, closer to the shock, the fluxes are observed to depend on energy. In this work, we analyze three interplanetary shock-related energetic particle events observed by the Advanced Composition Explorer spacecraft where flat ion energy spectra were observed upstream of the shock. We interpret these observations via a velocity filter mechanism for particles in a given energy range. This reveals that low energy particles tend to be confined to the shock front and cannot easily propagate upstream, while high energy particles can. The velocity filter mechanism has been corroborated from observations of particle flux anisotropy by the Solid-State Telescope of Wind/3DP.

Read this paper on arXiv…

S. Perri, G. Prete, G. Zimbardo, et. al.
Mon, 16 Jan 23
29/50

Comments: N/A

HST Low Resolution Stellar Library [SSA]

Posted on by

http://arxiv.org/abs/2301.05335


Hubble Space Telescope’s (HST) Space Telescope Imaging Spectrograph (STIS) targeted 556 stars in a long-running program called Next Generation Spectral Library (NGSL) via proposals GO9088, GO9786, GO10222, and GO13776. Exposures through three low resolution gratings provide wavelength coverage from 0.2 $< \lambda <$ 1 $\mu$m at $\lambda/\Delta\lambda\sim$ 1000, providing unique coverage in the ultraviolet (UV). The UV grating (G230LB) scatters red light and this results in unwanted flux that becomes especially troubling for cool stars. We applied scattered light corrections based on \cite{2022stis.rept….5W} and flux corrections arising from pointing errors relative to the center of the 0\farcs2 slit. We present 514 fully reduced spectra, fluxed, dereddened, and cross-correlated to zero velocity. Because of the broad spectral range, we can simultaneously study H$\alpha$ and Mg II $\lambda$2800, indicators of chromospheric activity. Their behaviours are decoupled. Besides three cool dwarfs and one giant with mild flares in H$\alpha$, only Be stars show strong H$\alpha$ emission. Mg2800 emission, however, strongly anti-correlates with temperature such that warm stars show absorption and stars cooler than $5000 : ! \rm{K}$ universally show chromospheric emission regardless of dwarf/giant status or metallicity. Transformed to Mg2800 flux emerging from the stellar surface, we find a correlation with temperature with approximately symmetric astrophysical scatter, in contrast to other workers who find a basal level with asymmetric scatter to strong values. Unsurprisingly, we confirm that Mg2800 activity is variable.

Read this paper on arXiv…

T. Pal, I. Khan, G. Worthey, et. al.
Mon, 16 Jan 23
32/50

Comments: 18 pages, 18 figures, 3 tables. Full version of table 3 is available online

On the Role of Interplanetary Shocks in Accelerating MeV Electrons [SSA]

Posted on by

http://arxiv.org/abs/2301.05587


One of the sources of solar energetic particle (SEP) events is shocks that are driven by fast coronal mass ejections (CMEs). They can accelerate SEPs up to relativistic energies and are attributed to the largest SEP events. New studies suggest that CME-driven shocks can potentially accelerate electrons to MeV energies in the vicinity of the Sun. We focus on relativistic electrons associated with strong IP shocks between 2007 and 2019 to determine whether the shocks can keep accelerating such electrons up to 1 AU distance. We have analyzed High Energy Telescope (HET) observations aboard the STEREO spacecraft of potential electron energetic storm particle (ESP) events, characterized by intensity time series that peak at the time of, or close to, the associated CME-driven shock crossing. We present a new filtering method to assess the statistical significance of particle intensity increases and apply it to MeV electron observations in the vicinity of interplanetary shocks. We identified 27 candidate events by visual inspection from a STEREO in-situ shock list. Our method identified nine clear cases, where a significant increase of MeV electrons was found in association with a shock. Typically, the highest statistical significance was observed in the highest HET energy channel of electrons. All nine cases were associated with shocks driven by interplanetary CMEs that showed large transit speeds, in excess of 900 km/s. In several cases multiple shocks were observed within one day of the shock related to the electron increase. Although electron ESP events at MeV energies are found to be rare at 1 AU our filtering method is not designed to identify a potential interplanetary shock contribution from distances closer to the Sun. Future observations taken during closer approaches to the Sun will likely provide clarity on interplanetary shock acceleration of electrons.

Read this paper on arXiv…

N. Sheshvan, N. Dresing, R. Vainio, et. al.
Mon, 16 Jan 23
33/50

Comments: 13 pages, submitted to A&A

A photometric study of NSVS 7453183: a probable quadruple system with long-term surface activity [SSA]

Posted on by

http://arxiv.org/abs/2301.05617


The $VRC$ light curves were regularly measured for the eclipsing binary NSVS 7453183 as a part of our long-term observational project for studying of low-mass eclipsing binaries with a short orbital period and surface activity. The TESS light curve solution in Phoebe results to the detached configuration, where the temperature of primary component was adopted to $T_1$ = 4300 K according to the SED approximation. It gives us $T_2 =$ 4080 $\pm$ 100 K for the secondary component. The spectral type of the primary component was estimated to be K6 and the photometric mass ratio was derived $q = 0.86$. We confirm presence of the third body in this system, a stellar companion with a minimal mass 0.33 M${\rm Sun}$ orbiting the eclipsing pair with a short period about 425 days, and propose the next, fourth body with a longer orbiting period of about 12 years, probably a brown dwarf with the minimal mass of 50 M${\rm Jup}$. The hierarchical structure ((1+1)+1)+1 of this quadruple system is assumed. Characteristics and temporal variations of the dark region on the surface of the primary component were estimated. The average migration speed of about 10 deg/month was found during years 2020-2022.

Read this paper on arXiv…

L. Šmelcer, M. Wolf, H. Kučáková, et. al.
Mon, 16 Jan 23
36/50

Comments: Accepted for publication in MNRAS. 11 pages, 9 figures, 9 tables. This is the authors’ version of the accepted manuscript

Surface magnetic field of the A-type metallic-line star omicron Pegasi revisited [SSA]

Posted on by

http://arxiv.org/abs/2301.05367


The bright A-type metallic-line star o Peg was reported in the early 1990s to have a surface magnetic field of ~2kG by analyzing the widths and strengths of spectral lines. In respect that those old studies were of rather empirical or approximate nature and the quality of observational data was not sufficient, this problem has been newly reinvestigated based on physically more rigorous simulations of line flux profiles, along with the observed equivalent widths (W) and full-widths at half-maximum (h) of 198 Fe I and 182 Fe II lines measured from the high-quality spectra. Given the Fe abundance derived from the conventional analysis, theoretical W and h values calculated for various sets of parameters were compared with the observed ones, which lead to the following conclusion regarding <H> (mean field strength). (1) An analysis of W yielded <H>~1-1.5kG from Fe II lines with the microturbulence of vt~1.5km/s. (2) A comparison of h resulted in <H>~1.5-2kG as well as the projected rotational velocity of vsini~5km/s. (3) Accordingly, the existence of mean magnetic field on the order of <H>~1-2kG in o Peg was confirmed, which is almost consistent with the consequence of the previous work.

Read this paper on arXiv…

Y. Takeda
Mon, 16 Jan 23
43/50

Comments: 17 pages including 10 figures and 4 tables (with supplementary materials); accepted for publication in Astronomishe Nachrichten

Data-Driven Selection and Spectral Classification of White Dwarf Stars [SSA]

Posted on by

http://arxiv.org/abs/2301.05209


The next generation of spectroscopic surveys is expected to provide spectra for hundreds of thousands of white dwarf (WD) candidates in the upcoming years. Currently, spectroscopic classification of white dwarfs is mostly done by visual inspection, requiring substantial amounts of expert attention. We propose a data-driven pipeline for fast, automatic selection and spectroscopic classification of WD candidates, trained using spectroscopically confirmed objects with available Gaia astrometry, photometry, and Sloan Digital Sky Survey (SDSS) spectra with signal-to-noise ratios $\geq9$. The pipeline selects WD candidates with improved accuracy and completeness over existing algorithms, classifies their primary spectroscopic type with $\gtrsim 90\%$ accuracy, and spectroscopically detects main sequence companions with similar performance. We apply our pipeline to the Gaia Data Release 3 cross-matched with the SDSS Data Release 17 (DR17), identifying 424 096 high-confidence WD candidates and providing the first catalogue of automated and quantifiable classification for 36 523 WD spectra. Both the catalogue and pipeline are made available online. Such a tool will prove particularly useful for the undergoing SDSS-V survey, allowing for rapid classification of thousands of spectra at every data release.

Read this paper on arXiv…

O. Vincent, P. Bergeron and P. Dufour
Fri, 13 Jan 23
6/72

Comments: Submitted to MNRAS (11 pages, 8 figures)

A DZ white dwarf with a 30 MG magnetic field [SSA]

Posted on by

http://arxiv.org/abs/2301.04665


Magnetic white dwarfs with field strengths below 10 MG are easy to recognise since the Zeeman splitting of spectral lines appears proportional to the magnetic field strength. For fields $\geq 100$ MG, however, transition wavelengths become chaotic, requiring quantum-chemical predictions of wavelengths and oscillator strengths with a non-perturbative treatment of the magnetic field. While highly accurate calculations have previously been performed for hydrogen and helium, the variational techniques employed become computationally intractable for systems with more than three to four electrons. Modern computational techniques, such as finite-field coupled-cluster theory, allow the calculation of many-electron systems in arbitrarily strong magnetic fields. Because around 25 percent of white dwarfs have metal lines in their spectra, and some of those are also magnetic, the possibility arises for some metals to be observed in very strong magnetic fields, resulting in unrecognisable spectra. We have identified SDSSJ114333.48+661531.83 as a magnetic DZ white dwarf, with a spectrum exhibiting many unusually shaped lines at unknown wavelengths. Using atomic data calculated from computational finite-field coupled-cluster methods, we have identified some of these lines arising from Na, Mg, and Ca. Surprisingly, we find a relatively low field strength of 30 MG, where the large number of overlapping lines from different elements make the spectrum challenging to interpret at a much lower field strength than for DAs and DBs. Finally we model the field structure of SDSSJ1143+6615 finding the data are consistent with an offset dipole.

Read this paper on arXiv…

M. Hollands, S. Stopkowicz, M. Kitsaras, et. al.
Fri, 13 Jan 23
13/72

Comments: 17 pages, 8 figures, Accepted for publication in MNRAS

Rotational modulation in A and F stars: Magnetic stellar spots or convective core rotation? [SSA]

Posted on by

http://arxiv.org/abs/2301.04974


The Kepler mission revealed a plethora of stellar variability in the light curves of many stars, some associated with magnetic activity or stellar oscillations. In this work, we analyse the periodic signal in 162 intermediate-mass stars, interpreted as Rossby modes and rotational modulation – the so-called \textit{hump \& spike} feature. We investigate whether the rotational modulation (\textit{spike}) is due to stellar spots caused by magnetic fields or due to Overstable Convective (OsC) modes resonantly exciting g~modes, with frequencies corresponding to the convective core rotation rate. Assuming that the spikes are created by magnetic spots at the stellar surface, we recover the amplitudes of the magnetic fields, which are in good agreement with theoretical predictions. Our data show a clear anti-correlation between the spike amplitudes and stellar mass and possibly a correlation with stellar age, consistent with the dynamo-generated magnetic fields theory in (sub)-surface convective layers. Investigating the harmonic behaviour, we find that for 125 stars neither of the two possible explanations can be excluded. While our results suggest that the dynamo-generated magnetic field scenario is more likely to explain the \textit{spike} feature, we assess further work is needed to distinguish between the two scenarios. One method for ruling out one of the two explanations is to directly observe magnetic fields in \textit{hump \& spike} stars. Another would be to impose additional constraints through detailed modelling of our stars, regarding the rotation requirement in the OsC mode scenario or the presence of a convective-core (stellar age).

Read this paper on arXiv…

A. Henriksen, V. Antoci, H. Saio, et. al.
Fri, 13 Jan 23
17/72

Comments: 18 pages, 28 figures

$δ$ Scuti pulsations in the bright Pleiades eclipsing binary HD 23642 [SSA]

Posted on by

http://arxiv.org/abs/2301.04912


We announce the discovery of pulsations in HD 23642, the only bright eclipsing system in the Pleiades, based on light curves from the Transiting Exoplanet Survey Satellite (TESS). We measure 46 pulsation frequencies and attribute them to delta Scuti pulsations in the secondary component. We find four l=1 doublets, three of which have frequency splittings consistent with the rotation rate of the star. The dipole mode amplitude ratios are consistent with a high stellar inclination angle and the stellar rotation period agrees with the orbital period. Together, these suggest that the spin axis of the secondary is aligned with the orbital axis. We also determine precise effective temperatures and a spectroscopic light ratio, and use the latter to determine the physical properties of the system alongside the TESS data and published radial velocities. We measure a distance to the system in agreement with the Gaia parallax, and an age of 170 +/- 20 Myr based on a comparison to theoretical stellar evolutionary models.

Read this paper on arXiv…

J. Southworth, S. Murphy and K. Pavlovski
Fri, 13 Jan 23
32/72

Comments: Accepted for publication as a Letter in MNRAS. 6 pages, 4 figures, 2 tables

Climbing the Cliffs: Classifying YSOs in the Cosmic Cliffs using a ML Approach with JWST Data [SSA]

Posted on by

http://arxiv.org/abs/2301.04772


The James Webb Space Telescope (JWST) observed a section of the star forming region NGC 3324 during its Early Release Observations. We make use of the Probabilistic Random Forest machine learning model to identify YSOs within the field of view. We build a matched catalog from photometry data products available on the Mikulski Space Telescope Archive and retrieve 8632 objects, of which Spitzer previously detected 458. We use previously classified data from Spitzer to train on a sample of the Webb data. We retrieve a total of 72 YSO candidates within the data field, 52 of which are only visible with JWST.

Read this paper on arXiv…

B. Crompvoets, H. Teimoorinia and J. Francesco
Fri, 13 Jan 23
37/72

Comments: N/A

The OGLE Collection of Variable Stars. Over 2600 Delta Scuti Stars in the Small Magellanic Cloud [SSA]

Posted on by

http://arxiv.org/abs/2301.04663


We present the first-ever collection of delta Scuti stars found over the entire area of the Small Magellanic Cloud (SMC). The sample consists of 2810 variables of which over 2600 objects belong to the SMC while the remaining stars are most likely members of the Milky Way’s halo. The sample has been divided into 2733 singlemode and 77 multimode pulsators. We provide observational parameters (pulsation periods, mean magnitudes, amplitudes, Fourier coefficients) of all delta Sct stars and the long-term I- and V-band time-series photometric measurements collected during the fourth phase of the Optical Gravitational Lensing Experiment (OGLE-IV).

Read this paper on arXiv…

I. Soszyński, A. Udalski, J. Skowron, et. al.
Fri, 13 Jan 23
38/72

Comments: 12 pages, 5 figures, submitted to Acta Astronomica

The Path from the Chinese and Japanese Observations of Supernova 1181 AD, to a Type Iax Supernova, to the Merger of CO and ONe White Dwarfs [SSA]

Posted on by

http://arxiv.org/abs/2301.04807


In 1181 AD, Chinese and Japanese observers reported a bright Guest Star' in the constellation Chuanshe, unmoving and visible for 185 days. In 2013, D. Patchick discovered a unique nebula surrounding a unique star, with two groups attributing this structure, namedPa 30′, to be the supernova remnant of SN 1181, as a sub-subclass of supernova, the low-luminosity Type Iax. Here, I provide a wide range of new observational evidence: First, a detailed analysis of the original Chinese and Japanese reports places the `Guest Star’ of 1181 into a small region with the only interesting source being Pa 30. Second, the ancient records confidently place the peak magnitude as 0.0 > V_peak > -1.4, and hence peak absolute magnitude of -14.5 > M_V,peak > -16.0 mag. Third, the Pa 30 central star is fading from B=14.90 in 1917, to B=16.20 in 1950, to B=16.58 in 2022. Fourth, recent light curves show typical variability with full-amplitude of 0.24 mag on time-scales of one day and longer, critically with no coherent modulations for periods from 0.00046–10 days to strict limits. Fifth, the spectral energy distribution from the far-infrared to the ultraviolet is a nearly perfect power-law with F_nu proportional to nu^(0.99 +- 0.07), observed luminosity of 128 +- 24 L_Sun, and absolute magnitude M_V = +1.07. I collect my new evidences with literature results to make a confident case to connect the Oriental observations to a supernova, then to Pa 30, then to a low-luminosity Type Iax SN, then to the only possible explosion mechanism as a merger between CO and ONe white dwarfs.

Read this paper on arXiv…

B. Schaefer
Fri, 13 Jan 23
42/72

Comments: MNRAS submitted

Shear-driven magnetic buoyancy in the solar tachocline: The mean electromotive force due to rotation [SSA]

Posted on by

http://arxiv.org/abs/2301.05067


The leading theoretical paradigm for the Sun’s magnetic cycle is an $\alpha\omega$-dynamo process, in which a combination of differential rotation and turbulent, helical flows produces a large-scale magnetic field that reverses every 11 years. Most $\alpha\omega$ solar dynamo models rely on differential rotation in the solar tachocline to generate a strong toroidal field. The most problematic part of such models is then the production of the large-scale poloidal field, via a process known as the $\alpha$-effect. Whilst this is usually attributed to small-scale convective motions under the influence of rotation, the efficiency of this regenerative process has been called into question by some numerical simulations. Motivated by likely conditions within the tachocline, the aim of this paper is to investigate an alternative mechanism for the poloidal field regeneration, namely the magnetic buoyancy instability in a shear-generated, rotating magnetic layer. We use a local, fully compressible model in which an imposed vertical shear winds up an initially vertical magnetic field. The field ultimately becomes buoyantly unstable, and we measure the resulting mean electromotive force (EMF). For sufficiently rapid rotation, we find that a significant component of the mean EMF is aligned with the direction of the mean magnetic field, which is the characteristic feature of the classical $\alpha\omega$-dynamo model. Our results therefore suggest that magnetic buoyancy could contribute directly to the generation of large-scale poloidal field in the Sun.

Read this paper on arXiv…

C. Duguid, P. Bushby and T. Wood
Fri, 13 Jan 23
43/72

Comments: Accepted for publication in MNRAS, 16 pages, 12 figures, 3 tables

First Detection of Radio Emission Associated with a Classical Cepheid [SSA]

Posted on by

http://arxiv.org/abs/2301.04666


We report the detection of 15 GHz radio continuum emission associated with the classical Cepheid variable star delta Cephei based on observations with the Karl G. Jansky Very Large Array. Our results constitute the first probable detection of radio continuum emission from a classical Cepheid. We observed the star at pulsation phase phi~0.43 (corresponding to the phase of maximum radius and minimum temperature) during three pulsation cycles in late 2018 and detected statistically significant emission (>5 sigma) during one of the three epochs. The observed radio emission appears to be variable at a >~10% level on timescales of days to weeks. We also present an upper limit on the 10 GHz flux density at pulsation phase phi=0.31 from an observation in 2014. We discuss possible mechanisms that may produce the observed 15 GHz emission, but cannot make a conclusive identification from the present data. The emission does not appear to be consistent with originating from a close-in, late-type dwarf companion, although this scenario cannot yet be strictly excluded. Previous X-ray observations have shown that delta Cephei undergoes periodic increases in X-ray flux during pulsation phase phi~0.43. The lack of radio detection in two out of three observing epochs at phi~0.43 suggests that either the radio emission is not linked with a particular pulsation phase, or else that the strength of the generated radio emission in each pulsation cycle is variable.

Read this paper on arXiv…

L. Matthews, N. Evans and M. Rupen
Fri, 13 Jan 23
44/72

Comments: 11 pages. Accepted to AJ

The Core Normal Type Ia Supernova 2019np: An Overall Spherical Explosion with an Aspherical Surface Layer and an Aspherical 56Ni Core [SSA]

Posted on by

http://arxiv.org/abs/2301.04721


Optical spectropolarimetry of the normal thermonuclear supernova SN2019np from -14.5 to +14.5 days relative to B-band maximum detected an intrinsic continuum polarization, p(cont), of 0.21+-0.09% at the first epoch. Between days -11.5 to +05, p(cont) remained about 0 and by day +14.5 was again significant at 0.19+-0.10%. Not considering the first epoch, the dominant axis of SiII(6355A) was roughly constant, staying close to the continuum until both rotated in opposite directions on day +14.5. Detailed radiation-hydrodynamical simulations produce a very steep density slope in the outermost ejecta so that the low first-epoch p(const) of about 0.2% nevertheless suggests a separate structure with an axis ratio of about 2 in the outer carbon-rich 3…5E-3 Mo. Large-amplitude fluctuations in the polarization profiles and a flocculent appearance of the polar diagram for the CaII near-infrared triplet (NIR3) may be related by a common origin. The temporal evolution of the polarization spectra agrees with an off-center delayed detonation. The late-time increase in polarization and the possible change in position angle are also consistent with an aspherical 56Ni core. The p(cont) and the absorptions due to Si II(6355A) and the CaII NIR3 form in the same region of the extended photosphere, with an interplay between line occultation and thermalization producing p. Small-scale polarization features may be due to small-scale structures, but many could be related to atomic patterns of the quasi-continuum; the hardly have an equivalent in the total-flux spectrum. We compare SN2019np to other SNe and develop future objectives and strategies for SNIa spectropolarimetry.

Read this paper on arXiv…

P. Hoeflich, Y. Yang, D. Baade, et. al.
Fri, 13 Jan 23
48/72

Comments: 23 pages, 18 figures, 2 tables, MNRAS, submitted 11/9/22, revised 12/9/22

A study of the rapid rotator $ζ$ Aql: differential surface rotation? [SSA]

Posted on by

http://arxiv.org/abs/2301.05018


We report new, extremely precise, photopolarimetry of the rapidly-rotating A0 main-sequence star $\zeta$ Aql, covering the wavelength range $\sim$400–900nm, which reveals a rotationally-induced signal. We model the polarimetry, together with the flux distribution and line profiles, in the framework of Roche geometry with $\omega$-model gravity darkening, to establish the stellar parameters. An additional constraint is provided by TESS photometry, which shows variability with a period, $P_{\rm phot}$, of 11.1 hr. Modelling based on solid-body surface rotation gives rotation periods, $P_{\rm rot}$, that are in only marginal agreement with this value. We compute new ESTER stellar-structure models to predict horizontal surface velocity fields, which depart from solid-body rotation at only the $\sim$2% level (consistent with a reasonably strong empirical upper limit on differential rotation derived from the line-profile analysis). These models bring the equatorial rotation period, $P_{\rm rot,e}$, into agreement with $P_{\rm phot}$, without requiring any ‘fine tuning’ (for the Gaia parallax). We confirm that surface abundances are significantly subsolar ($\mbox{[M/H]} \simeq -0.5$). The star’s basic parameters are established with reasonably good precision: ${M = 2.53\pm0.16\,\mbox{M}\odot}$, $\log{L/\mbox{L}\odot} = 1.82\pm0.02$, $R_{\rm p} = 2.21\pm 0.02\,\mbox{R}\odot$, $T{\rm eff} = 9693 \pm 50~\mbox{K}$, $i = 85{^{+5}{-7}}^\circ$, and $\omega/\omega{\rm c} = 0.95\pm0.02$. Comparison with single-star, solar-abundance stellar-evolution models incorporating rotational effects shows excellent agreement (but somewhat poorer agreement for models at $\mbox{[M/H]} \simeq -0.4$).

Read this paper on arXiv…

I. Howarth, J. Bailey, D. Cotton, et. al.
Fri, 13 Jan 23
59/72

Comments: MNRAS, accepted

Why the observed spin evolution of older-than-solar like stars might not require a dynamo mode change [SSA]

Posted on by

http://arxiv.org/abs/2301.04693


The spin evolution of main sequence stars has long been of interest for basic stellar evolution, stellar aging, stellar activity, and consequent influence on companion planets. Observations of older than solar late-type main-sequence stars have been interpreted to imply that a change from a dipole-dominated magnetic field to one with more prominent higher multipoles might be necessary to account for the data. The spin-down models that lead to this inference are essentially tuned to the sun. Here we take a different approach which considers individual stars as fixed points rather than just the Sun. We use a time-dependent theoretical model to solve for the spin evolution of low-mass main-sequence stars that includes a Parker-type wind and a time-evolving magnetic field coupled to the spin. Because the wind is exponentially sensitive to the stellar mass over radius and the coronal base temperature, the use of each observed star as a separate fixed point is more appropriate and, in turn, produces a set of solution curves that produces a solution envelope rather than a simple line. This envelope of solution curves, unlike a single line fit, is consistent with the data and does not unambiguously require a modal transition in the magnetic field to explain it. Also, the theoretical envelope does somewhat better track the older star data when thermal conduction is a more dominant player in the corona.

Read this paper on arXiv…

K. Kotorashvili, E. Blackman and J. Owen
Fri, 13 Jan 23
68/72

Comments: 8 pages, 4 figures; submitted to MNRAS

Coronal Loop Heating by Nearly Incompressible Magnetohydrodynamic and Reduced Magnetohydrodynamic Turbulence Models [SSA]

Posted on by

http://arxiv.org/abs/2301.04319


The transport of waves and turbulence beyond the photosphere is central to the coronal heating problem. Turbulence in the quiet solar corona has been modeled on the basis of the nearly incompressible magnetohydrodynamic (NI MHD) theory to describe the transport of low-frequency turbulence in open magnetic field regions. It describes the evolution of the coupled majority quasi-2D and minority slab component, driven by the magnetic carpet and advected by a subsonic, sub-Alfvenic flow from the lower corona. In this paper, we couple the NI MHD turbulence transport model with an MHD model of the solar corona to study the heating problem in a coronal loop. In a realistic benchmark coronal loop problem, we find that a loop can be heated to ~1.5 million K by transport and dissipation of MHD turbulence described by the NI MHD model. We also find that the majority 2D component is as important as the minority slab component in the heating of the coronal loop. We compare our coupled MHD/NI MHD model results with a reduced MHD (RMHD) model. An important distinction between these models is that RMHD solves for small-scale velocity and magnetic field fluctuations and obtains the actual viscous/resistive dissipation associated with their evolution whereas NI MHD evolves scalar moments of the fluctuating velocity and magnetic fields and approximates dissipation using an MHD turbulence phenomenology. Despite the basic differences between the models, their simulation results match remarkably well, yielding almost identical heating rates inside the corona.

Read this paper on arXiv…

M. Yalim, G. Zank and M. Asgari-Targhi
Thu, 12 Jan 23
9/68

Comments: 23 pages, 6 figures, 1 table, The Astrophysical Journal, in press

Comprehensive spectroscopic and photometric study of pulsating eclipsing binary star AI Hya [SSA]

Posted on by

http://arxiv.org/abs/2301.04409


The pulsating eclipsing binaries are remarkable systems that provide an opportunity to probe the stellar interior and to determine the fundamental stellar parameters precisely. Especially the detached eclipsing binary systems with (a) pulsating component(s) are significant objects to understand the nature of the oscillations since the binary effects in these systems are negligible. Recent studies based on space data have shown that the pulsation mechanisms of some oscillating stars are not completely understood. Hence, comprehensive studies of a number of pulsating stars within detached eclipsing binaries are important. In this study, we present a detailed analysis of the pulsating detached eclipsing binary system AI Hya which was studied by two independent groups with different methods. We carried out a spectroscopic survey to estimate the orbital parameters via radial velocity measurements and the atmospheric parameters of each binary component using the composite and/or disentangled spectra. We found that the more luminous component of the system is a massive, cool and chemically normal star while the hotter binary component is a slightly metal-rich object. The fundamental parameters of AI Hya were determined by the analysis of binary variations and subsequently used in the evolutionary modelling. Consequently, we obtained the age of the system as 850 $\pm$ 20 Myr and found that both binary components are situated in the Delta Scuti instability strip. The frequency analysis revealed pulsation frequencies between the 5.5 – 13.0 d$^{-1}$ and we tried to estimate which binary component is the pulsating one. However, it turned out that those frequencies could originate from both binary components.

Read this paper on arXiv…

F. Alivacus, T. Pawar, K. Hełminiak, et. al.
Thu, 12 Jan 23
16/68

Comments: Accepted for publication in MNRAS

Optimal observational scheduling framework for binary and multiple stellar systems [SSA]

Posted on by

http://arxiv.org/abs/2301.04162


The optimal instant of observation of astrophysical phenomena for objects that vary on human time-sales is an important problem, as it bears on the cost-effective use of usually scarce observational facilities. In this paper we address this problem for the case of tight visual binary systems through a Bayesian framework based on the maximum entropy sampling principle. Our proposed information-driven methodology exploits the periodic structure of binary systems to provide a computationally efficient estimation of the probability distribution of the optimal observation time. We show the optimality of the proposed sampling methodology in the Bayes sense and its effectiveness through direct numerical experiments. We successfully apply our scheme to the study of two visual-spectroscopic binaries, and one purely astrometric triple hierarchical system. We note that our methodology can be applied to any time-evolving phenomena, a particularly interesting application in the era of dedicated surveys, where a definition of the cadence of observations can have a crucial impact on achieving the science goals.

Read this paper on arXiv…

M. Videla, R. Mendez, J. Silva, et. al.
Thu, 12 Jan 23
19/68

Comments: Accepted for publication to PASP. 23 pages, 2 Tables, 9 Figures, 2 Appendices