Characterization of methanol as a magnetic field tracer in star-forming regions [GA]

http://arxiv.org/abs/1802.05764


Magnetic fields play an important role during star formation. Direct magnetic field strength observations have proven specifically challenging in the extremely dynamic protostellar phase. Because of their occurrence in the densest parts of star forming regions, masers, through polarization observations, are the main source of magnetic field strength and morphology measurements around protostars. Of all maser species, methanol is one of the strongest and most abundant tracers of gas around high-mass protostellar disks and in outflows. However, as experimental determination of the magnetic characteristics of methanol has remained largely unsuccessful, a robust magnetic field strength analysis of these regions could hitherto not be performed. Here we report a quantitative theoretical model of the magnetic properties of methanol, including the complicated hyperfine structure that results from its internal rotation. We show that the large range in values of the Land\'{e} g-factors of the hyperfine components of each maser line lead to conclusions which differ substantially from the current interpretation based on a single effective g-factor. These conclusions are more consistent with other observations and confirm the presence of dynamically important magnetic fields around protostars. Additionally, our calculations show that (non-linear) Zeeman effects must be taken into account to further enhance the accuracy of cosmological electron-to-proton mass ratio determinations using methanol.

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B. Lankhaar, W. Vlemmings, G. Surcis, et. al.
Mon, 19 Feb 18
8/41

Comments: 23 pages, 3 figures, excluding Supplementary information. Author manuscript version before editorial/copyediting by Nature Astronomy. Journal version available via this http URL . Supplementary material available via this https URL

AD Leonis: Radial velocity signal of stellar rotation or spin-orbit resonance? [EPA]

http://arxiv.org/abs/1802.06064


AD Leonis is a nearby magnetically active M dwarf. We find Doppler variability with a period of 2.23 days as well as photometric signals: (1) a short period signal which is similar to the radial velocity signal albeit with considerable variability; and (2) a long term activity cycle of 4070$\pm$120 days. We examine the short-term photometric signal in the available ASAS and MOST photometry and find that the signal is not consistently present and varies considerably as a function of time. This signal undergoes a phase change of roughly 0.8 rad when considering the first and second halves of the MOST data set which are separated in median time by 3.38 days. In contrast, the Doppler signal is stable in the combined HARPS and HIRES radial velocities for over 4700 days and does not appear to vary in time in amplitude, phase, period or as a function of extracted wavelength. We consider a variety of star-spot scenarios and find it challenging to simultaneously explain the rapidly varying photometric signal and the stable radial velocity signal as being caused by starspots co-rotating on the stellar surface. This suggests that the origin of the Doppler periodicity might be the gravitational tug of a planet orbiting the star in spin-orbit resonance. For such a scenario and no spin-orbit misalignment, the measured $v \sin i$ indicates an inclination angle of 15.5$\pm$2.5 deg and a planetary companion mass of 0.237$\pm$0.047 M$_{\rm Jup}$.

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M. Tuomi, H. Jones, G. Anglada-Escude, et. al.
Mon, 19 Feb 18
9/41

Comments: 19 pages (incl. example data tables), accepted for publication in AJ

A dual origin for water in carbonaceous asteroids revealed by CM chondrites [EPA]

http://arxiv.org/abs/1802.05893


Carbonaceous asteroids represent the principal source of water in the inner Solar System and might correspond to the main contributors for the delivery of water to Earth. Hydrogen isotopes in water-bearing primitive meteorites, e.g. carbonaceous chondrites, constitute a unique tool for deciphering the sources of water reservoirs at the time of asteroid formation. However, fine-scale isotopic measurements are required to unravel the effects of parent body processes on the pre-accretion isotopic distributions. Here we report in situ micrometer-scale analyses of hydrogen isotopes in six CM-type carbonaceous chondrites revealing a dominant deuterium-poor water component ({\delta}D = -350 +/- 40 permil) mixed with deuterium-rich organic matter. We suggest that this D-poor water corresponds to a ubiquitous water reservoir in the inner protoplanetary disk. A deuterium-rich water signature has been preserved in the least altered part of the Paris chondrite ({\delta}DParis > -69 +/- 163 permil) in hydrated phases possibly present in the CM rock before alteration. The presence of the D-enriched water signature in Paris might indicate that transfers of ice from the outer to the inner Solar System have been significant within the first million years of the Solar System history.

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L. Piani, H. Yurimoto and L. Remusat
Mon, 19 Feb 18
10/41

Comments: 20 pages, 3 figures, 2 tables

Gamma rays from Dark Matter Annihilation in Three-loop Radiative Neutrino Mass Generation Models [CL]

http://arxiv.org/abs/1802.05971


We present the Sommerfeld enhanced Dark Matter (DM) annihilation into gamma ray for a class of three-loop radiative neutrino mass models with large electroweak multiplets where the DM mass is in O(TeV) range. We show that in this model, the DM annihilation rate becomes more prominent for larger multiplets and it is already within the reach of currently operating Imaging Atmospheric Cherenkov telescopes (IACTs), High Energy Stereoscopic System (H.E.S.S.). Furthermore, Cherenkov Telescope Array (CTA), which will begin operating in 2030, will improve this sensitivity by a factor of $\mathcal{O}{(10)}$ and may exclude a large portion of parameter space of this radiative neutrino mass model with larger electroweak multiplet. This implies that the only viable option is the model with lowest electroweak multiplets i.e. singlets of $SU(2)_{L}$ where the DM annihilation rate is not Sommerfeld enhanced and hence it is not yet constrained by the indirect detection limits from H.E.S.S. or future CTA.

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T. Chowdhury and S. Nasri
Mon, 19 Feb 18
11/41

Comments: 12 pages, 7 figures

Impacts of nuclear-physics uncertainties in the s-process determined by Monte-Carlo variations [SSA]

http://arxiv.org/abs/1802.05836


The s-process, a production mechanism based on slow-neutron capture during stellar evolution, is the origin of about half the elements heavier than iron. Abundance predictions for s-process nucleosynthesis depend strongly on the relevant neutron-capture and $\beta$-decay rates, as well as on the details of the stellar model being considered. Here, we have used a Monte-Carlo approach to evaluate the nuclear uncertainty in s-process nucleosynthesis. We considered the helium burning of massive stars for the weak s-process and low-mass asymptotic-giant-branch stars for the main s-process. Our calculations include a realistic and general prescription for the temperature dependent uncertainty for the reaction cross sections. We find that the adopted uncertainty for (${\rm n},\gamma$) rates, tens of per cent on average, effects the production of s-process nuclei along the line of $\beta$-stability, and that the uncertainties in $\beta$-decay from excited state contributions, has the strongest impact on branching points.

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N. Nishimura, G. Cescutti, R. Hirschi, et. al.
Mon, 19 Feb 18
12/41

Comments: 6 pages, 4 figures, 2 tables, the Proceedings of “the 2017 Symposium on Nuclear Data”; a supplementary article of arXiv:1701.00489

Beryllium detection in the very fast nova ASASSN-16kt (V407 Lupi) [SSA]

http://arxiv.org/abs/1802.05896


We present high-resolution spectroscopic observations of the fast nova ASASSN-16kt (V407 Lup). A close inspection of spectra obtained at early stages has revealed the presence of low-ionization lines, and among the others we have identified the presence of the ionised $^7$Be doublet in a region relatively free from possible contaminants. After studying their intensities, we have inferred that ASASSN-16kt has produced (5.9 – 7.7)$ \times 10^{-9}$ M${\odot}$ of $^7$Be. The identification of bright Ne lines may suggest that the nova progenitor is a massive (1.2 M${\odot}$) oxygen-neon white dwarf. The high outburst frequency of oxygen-neon novae implies that they likely produce an amount of Be similar, if not larger, to that produced by carbon-oxygen novae, then confirming that classical novae are among the main factories of lithium in the Galaxy.

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L. Izzo, P. Molaro, P. Bonifacio, et. al.
Mon, 19 Feb 18
13/41

Comments: 11 pages, 8 figures, 4 tables. Accepted for publication in MNRAS

Duty-cycle and energetics of remnant radio-loud AGN [GA]

http://arxiv.org/abs/1802.05806


Deriving the energetics of remnant and restarted active galactic nuclei (AGNs) is much more challenging than for active sources due to the complexity in accurately determining the time since the nucleus switched-off. I resolve this problem using a new approach that combines spectral ageing and dynamical models to tightly constrain the energetics and duty-cycles of dying sources. Fitting the shape of the integrated radio spectrum yields the fraction of the source age the nucleus is active; this, in addition to the flux density, source size, axis ratio, and properties of the host environment, provides a constraint on dynamical models describing the remnant radio source. This technique is used to derive the intrinsic properties of the well-studied remnant radio source B2 0924+30. This object is found to spend $50^{+14}{-12}$ Myr in the active phase and a further $28^{+6}{-5}$ Myr in the quiescent phase, have a jet kinetic power of $3.6^{+3.0}_{-1.7}\times 10^{37}$ W, and a lobe magnetic field strength below equipartition at the $8\sigma$ level. The integrated spectra of restarted and intermittent radio sources is found to yield a ‘steep-shallow’ shape when the previous outburst occurred within 100 Myr. The duty-cycle of B2 0924+30 is hence constrained to be $\delta < 0.15$ by fitting the shortest time to the previous comparable outburst that does not appreciably modify the remnant spectrum. The time-averaged feedback energy imparted by AGNs into their host galaxy environments can in this manner be quantified.

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R. Turner
Mon, 19 Feb 18
14/41

Comments: 9 pages, 5 figures, 1 table; accepted in MNRAS