分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yutong Shan
Ansgar Reiners
Damian Fabbian
Emilio Marfil
David Montes
Hugo M. Tabernero
Ignasi Ribas
Jose A. Caballero
Andreas Quirrenbach
Pedro J. Amado
Jesus Aceituno
Victor J. S. Bejar
Miriam Cortes-Contreras
Stefan Dreizler
Artie P. Hatzes
Thomas Henning
Sandra V. Jeffers
Adrian Kaminski
Martin Kurster
Marina Lafarga
摘要： (Abridged) We characterize a series of neutral vanadium atomic absorption lines in the 800--910nm wavelength region of high signal-to-noise, high-resolution, telluric-corrected M-dwarf spectra from the CARMENES survey. Many of these lines are prominent and exhibit a distinctive broad and flat-bottom shape, which is a result of hyperfine structure (HFS). We investigate the potential and implications of these HFS split lines for abundance analysis of cool stars. With standard spectral synthesis routines, as provided by the spectroscopy software iSpec and the latest atomic data (including HFS) available from the VALD3 database, we modeled these striking line profiles. We used them to measure V abundances of cool dwarfs. We determined V abundances for 135 early M dwarfs (M0.0V to M3.5V) in the CARMENES guaranteed time observations sample. They exhibit a [V/Fe]-[Fe/H] trend consistent with that derived from nearby FG dwarfs. The tight ($\pm$ 0.1 dex) correlation between [V/H] and [Fe/H] suggests the potential application of V as an alternative metallicity indicator in M dwarfs. We also show hints that neglecting to model HFS could partially explain the temperature correlation in V abundance measurements observed in previous studies of samples involving dwarf stars with $T_{\rm eff} \lesssim 5300$K. Our work suggests that HFS can impact certain absorption lines in cool photospheres more severely than in Sun-like ones. Therefore, we advocate that HFS should be carefully treated in abundance studies in stars cooler than $\sim 5000$K. On the other hand, strong HFS split lines in high-resolution spectra present an opportunity for precision chemical analyses of large samples of cool stars. The V-to-Fe trends exhibited by the local M dwarfs continue to challenge theoretical models of V production in the Galaxy.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Tsevi Mazeh
Simchon Faigler
Dolev Bashi
Sahar Shahaf
Niv Davidson
Matthew Green
Roy Gomel
Dan Maoz
Amitay Sussholz
Subo Dong
Haotong Zhang
Jifeng Liu
Song Wang
Ali Luo
Zheng Zheng
Na'ama Hallakoun
Volker Perdelwitz
David W. Latham
Ignasi Ribas
David Baroch
摘要： We have identified 2XMM J125556.57+565846.4, at a distance of 600 pc, as a binary system consisting of a normal star and a probable dormant neutron star. Optical spectra exhibit a slightly evolved F-type single star, displaying periodic Doppler shifts with a 2.76-day Keplerian circular orbit, with no indication of light from a secondary component. Optical and UV photometry reveal ellipsoidal variations with half the orbital period, due to the tidal deformation of the F star. The mass of the unseen companion is constrained to the range $1.1$--$2.1\,M_{\odot}$ at $3\sigma$ confidence, with the median of the mass distribution at $1.4\,M_{\odot}$, the typical mass of known neutron stars. A main-sequence star cannot masquerade as the dark companion. The distribution of possible companion masses still allows for the possibility of a very massive white dwarf. The companion itself could also be a close pair consisting of a white dwarf and an M star, or two white dwarfs, although the binary evolution that would lead to such a close triple system is unlikely. Similar ambiguities regarding the certain identification of a dormant neutron star are bound to affect most future discoveries of this type of non-interacting system. If the system indeed contains a dormant neutron star, it will become, in the future, a bright X-ray source and afterwards might even host a millisecond pulsar.
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