Characterising abundance-age relations of GALAH stars using oxygen-enhanced stellar models
| Autor: | Tiancheng Sun, Xunzhou Chen, Shaolan Bi, Zhishuai Ge, Maosheng Xiang, Yaqian Wu |
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| Rok vydání: | 2023 |
| Předmět: | |
| Zdroj: | Monthly Notices of the Royal Astronomical Society. |
| ISSN: | 1365-2966 0035-8711 |
| DOI: | 10.1093/mnras/stad1499 |
| Popis: | Main Sequence Turn-off stars (MSTO) and subgiant stars are good tracers of galactic populations. We present a study of 41,034 MSTO and subgiant stars from the GALAH survey. Using a grid of stellar models that accounts for the variation of O abundances, we determine their ages with a median age uncertainty of $\sim$9.4 per cent. Our analysis reveals that the ages of high-O stars based on O-enhanced models (OEM models) are smaller than those determined with $\alpha$-enhanced models, resulting in a mean fractional age difference of -5.3 per cent at [O/$\alpha$] = 0.2 and -11.0 per cent at [O/$\alpha$] = 0.4. This age difference significantly impacts the age distribution of thick disc and halo stars, leading to a steeper downward trend in the [Fe/H]-age plane from 8 Gyr to 14 Gyr, indicating a shorter formation time-scale and a faster chemical-enhanced history for these populations. We confirm the V-shape of the normalized age-metallicity distribution $p$($\tau$$\mid$[Fe/H]) of thin disc stars, which is presumably a consequence of the second gas infall. Additionally, we find that the halo stars in our sample can be divided into two sequences, a metal-rich sequence (Splash stars) and a metal-poor sequence (accreted stars), with the Splash stars predominantly older than 9 Gyr and the accreted halo stars older than 10 Gyr. Finally, we observe two distinct sequences in the relations between various chemical abundances and age for disc stars, namely a young sequence with ages $$ $\sim$8 Gyr. Comment: 11 pages, 12 figures |
| Databáze: | OpenAIRE |
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