The accreted galaxy: An overview of TESS metal-poor accreted star candidates

¹ Instituto de Estudiols Astrofísicos, Facultad de Ingeniería y Ciencias, Univesidad Diego Portales, Santiago de Chile, Chile
² Millennium Nucleus ERIS, Santiago, Chile
³ School of Physical and Chemical Sciences – Te Kura Matu, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand
⁴ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁵ Department of Astronomy, The University of Texas at Austin, 2515 Speedway Boulevard, Austin, TX 78712, USA
⁶ Department of Physics, University of Surrey, Stag Hill, Guildford, GU2 7XH Guildford, UK

^★ Corresponding author; danielle.debrito@mail.udp.cl

Received: 4 May 2024
Accepted: 26 July 2024

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 are 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 surface gravity (log ɡ) values and values obtained using spectroscopy, demonstrating the reliability of spectroscopic data produced by our methodology. We find 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 ɡ. However, we find that calcium (Ca) abundances are more sensitive to the adopted log ɡ. Our study reveals that the majority of our stars have properties that are compatible with those reported for the Gai’a-Sausage-Enceladus, with a minority of stars that might be associated with Splash. We find an age distribution with a median of 11.3_−4.1^+1.3 Gyr when including asteroseismic information. Regarding some key chemical signatures, we note that these stars are metal poor ([Fe/H]) < −0.8), α rich ([α]/Fe] > 0.2), and copper poor ([Cu/Fe] < 0 ), with chemical abundances typical of accreted stars. These findings illustrate the importance of multidimensional analyses in unraveling the complex accretion history of the Milky Way.