On the Origin of Metal-poor Stars in the Solar Neighborhood

Abstract

We determined the ages, kinematic parameters, and Galactic orbital parameters of six metal-poor (−2.4 < [Fe/H] < −1.0 dex), F-type, high-proper-motion (HPM) stars to investigate their HPM nature and origin. For the kinematical procedure, the astrometric data from the Gaia DR2 were used. High-resolution ELODIE spectra of the six dwarfs were also used to obtain accurate [Fe/H] abundances and up-to-date [α/Fe] abundances. The calculations for stellar ages were based on Bayesian statistics, with the computed ages falling in the range 9.5–10.1 Gyr. On the basis of the metallicities and ages, six HMP stars are either members of the halo (HD 6755, HD 84937, BD +42 3607) or members of the low-metallicity tail of the thick disk (HD 3567, HD 194598, HD 201891). However, Galactic orbital parameters suggest thin disk (HD 84937, HD 194598), thick disk (HD 3567, HD 201891), and halo (HD 6755, BD +42 3607) populations. The dynamical analysis was also performed for the escape scenario from the candidate GCs. The tidal disruption of a dwarf galaxy was also considered as an alternative origin. HD 6755, HD 194598, and HD 3567, with their retrograde orbital motions, are likely candidate stars for a tidally disrupted dwarf galaxy origin. However, the relationship of HD 194598 with NGC 6284 presents an interesting case. Its encounter velocity is low (16 ± 28 km s−1), and their ages and metallicities are very nearly consistent with each other at the 1σ level. The rest of the HPM sample stars have a 4%–18% probability of encountering with selected GCs for 1.5 tidal radii. This indicates that a globular cluster origin for the program stars is unlikely.

Spectral evidence of solar neighborhood analogs in CALIFA galaxies

“…Even though the global properties explored above have restricted the type of galaxies in which SNA are likely to be found, local properties have the potential to unveil the environmental physics of such regions. The local conditions of the SN have been widely studied in recent years and we have revealed a clear picture of our vicinity through a wide variety of stellar tracers (e. g., Bonatto & Bica 2011;Sollima 2019;Şahin & Bilir 2020;Whitten et al 2021;Gontcharov & Mosenkov 2021, to name a few). The SN is known to be in an expanding local under- et al 2007).…”

Hyperfine Structure Investigation of Singly Ionized Thulium in Fourier-transform Spectra

“…The transition probabilities for these lines were also obtained from Sneden et al (2009). Details on model atmosphere computation and synthesis were described in Şahin et al (2011Şahin et al ( ), Şahin et al (2016Şahin et al ( ), and Şahin & Bilir (2020. The best fits in the wavelength regions around the Tm II lines in the three spectra are shown in Figure 1 and Figure 2.…”