The accreted Galaxy: An overview of TESS metal-poor accreted stars candidates

TL;DR

This study investigates metal-poor accreted stars in the Milky Way using TESS, Gaia, and spectroscopic data to understand their properties, ages, and chemical signatures, shedding light on the galaxy's accretion history.

Contribution

It provides a detailed analysis of 30 accreted star candidates, highlighting the impact of asteroseismic data on age and chemical abundance determinations, and characterizes their origins.

Findings

Most stars are compatible with Gaia-Sausage-Enceladus origin.

Median age of stars is 11.3 Gyr with uncertainties.

Chemical signatures are consistent with accreted, metal-poor, alpha-rich stars.

Abstract

The Milky Way is a mosaic of stars from different origins. In particular, metal-poor accreted star candidates offer a unique opportunity to better understand the accretion history of the Milky Way. In this work, we aim to explore the assembly history of the Milky Way by investigating accreted stars in terms of their ages, dynamical properties, and chemical abundances. We also aim to better characterize the impact of incorporating asteroseismic information on age and chemical abundance calculations of metal-poor accreted stars for which TESS data is available. In this study, we conducted an in-depth examination of 30 metal-poor accreted star candidates, using TESS and Gaia data, as well as MIKE spectra. We find satisfactory agreement between seismic and predicted/spectroscopic surface gravity (log g) values, demonstrating the reliability of spectroscopic data from our methodology. We found that while age determination is highly dependent on the log g and asteroseismic information used, the overall chemical abundance distributions are similar for different log g. However, we found that calcium (Ca) abundances are more sensitive to the adopted log g. Our study reveals that the majority of our stars have properties compatible to those reported for the Gaia-Sausage-Enceladus, with a minority of stars that might be associated to Splash. We found an age distribution with a median of 11.3 Gyr with lower and upper uncertainties of 4.1 and 1.3 Gyr respectively when including asteroseismic information. As regarding some key chemical signatures we note that these stars are metal-poor ([Fe/H]) < -0.8), alpha-rich ([alpha]/Fe] > 0.2), copper-poor ([Cu/Fe] < 0 ) and with chemical abundances typical of accreted stars. These findings illustrate the importance of multi-dimensional analyses in unraveling the complex accretion history of the Milky Way.