スダ　タクマ   Takuma SUDA   須田　拓馬    所属   学環 教養学環    職種   准教授
言語種別	英語
発行・発表の年月	2021/05
形態種別	学術論文
査読	査読あり
標題	Star Formation Timescales of the Halo Populations from Asteroseismology and Chemical Abundances
執筆形態	共著
掲載誌名	The Astrophysical Journal
掲載区分	国外
出版社・発行元	IOP Publishing
巻・号・頁	912,pp.72
総ページ数	38
著者・共著者	Tadafumi Matsuno, Wako Aoki, Luca Casagrande, Miho N. Ishigaki, Jianrong Shi, Masao Takata, Maosheng Xiang, David Yong, Haining Li, Takuma Suda
概要	We combine asteroseismology, optical high-resolution spectroscopy, and kinematic analysis for 26 halo red giant branch stars in the Kepler field in the range of −2.5 < [Fe/H] < −0.6. After applying theoretically motivated corrections to the seismic scaling relations, we obtain an average mass of 0.97 ± 0.03 M⊙ for our sample of halo stars. Although this maps into an age of ~7 Gyr, significantly younger than independent age estimates of the Milky Way stellar halo, we considered this apparently young age to be due to the overestimation of stellar mass in the scaling relations. There is no significant mass dispersion among lower red giant branch stars (log g > 2), which constrains the relative age dispersion to <18%, corresponding to <2 Gyr. The precise chemical abundances allow us to separate the stars with [Fe/H] > −1.7 into two [Mg/Fe] groups. While the [α/Fe] and [Eu/Mg] ratios are different between the two subsamples, [s/Eu], where s stands for Ba, La, Ce, and Nd, does not show a significant difference. These abundance ratios suggest that the chemical evolution of the low-Mg population is contributed by Type Ia supernovae, but not by low- to intermediate-mass asymptotic giant branch stars, providing a constraint on its star formation timescale as 100 Myr < τ < 300 Myr. We also do not detect any significant mass difference between the two [Mg/Fe] groups, thus suggesting that their formation epochs are not separated by more than 1.5 Gyr.
DOI	10.3847/1538-4357/abeab2
arXiv ID	arXiv:2006.03619
外部リンクURL	https://ui.adsabs.harvard.edu/abs/2021ApJ...912...72M/abstract