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The GALAH survey: tracing the Milky Way's formation and evolution through RR Lyrae stars.

Authors :
D'Orazi, Valentina
Storm, Nicholas
Casey, Andrew R
Braga, Vittorio F
Zocchi, Alice
Bono, Giuseppe
Fabrizio, Michele
Sneden, Christopher
Massari, Davide
Giribaldi, Riano E
Bergemann, Maria
Campbell, Simon W
Casagrande, Luca
de Grijs, Richard
De Silva, Gayandhi
Lugaro, Maria
Zucker, Daniel B
Bragaglia, Angela
Feuillet, Diane
Fiorentino, Giuliana
Source :
Monthly Notices of the Royal Astronomical Society. Jun2024, Vol. 531 Issue 1, p137-162. 26p.
Publication Year :
2024

Abstract

Stellar mergers and accretion events have been crucial in shaping the evolution of the Milky Way (MW). These events have been dynamically identified and chemically characterized using red giants and main-sequence stars. RR Lyrae (RRL) variables can play a crucial role in tracing the early formation of the MW since they are ubiquitous, old (t ≥ 10 Gyr) low-mass stars and accurate distance indicators. We exploited Data Release 3 of the GALAH survey to identify 78 field RRLs suitable for chemical analysis. Using synthetic spectra calculations, we determined atmospheric parameters and abundances of Fe, Mg, Ca, Y, and Ba. Most of our stars exhibit halo-like chemical compositions, with an iron peak around [Fe/H] ≈ −1.40, and enhanced Ca and Mg content. Notably, we discovered a metal-rich tail, with [Fe/H] values ranging from −1 to approximately solar metallicity. This sub-group includes almost 1/4 of the sample, it is characterized by thin disc kinematics and displays sub-solar α-element abundances, marginally consistent with the majority of the MW stars. Surprisingly, they differ distinctly from typical MW disc stars in terms of the s-process elements Y and Ba. We took advantage of similar data available in the literature and built a total sample of 535 field RRLs for which we estimated kinematical and dynamical properties. We found that metal-rich RRLs (1/3 of the sample) likely represent an old component of the MW thin disc. We also detected RRLs with retrograde orbits and provided preliminary associations with the Gaia–Sausage–Enceladus, Helmi, Sequoia, Sagittarius, and Thamnos stellar streams. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
00358711
Volume :
531
Issue :
1
Database :
Academic Search Index
Journal :
Monthly Notices of the Royal Astronomical Society
Publication Type :
Academic Journal
Accession number :
177681455
Full Text :
https://doi.org/10.1093/mnras/stae1149