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

Autor(en)

Valentina D’Orazi, Nicholas Storm, Andrew R. Casey, Vittorio F. Braga, Alice Zocchi, Giuseppe Bono, Michele Fabrizio, Christopher Sneden, Davide Massari, Riano E. Giribaldi, Maria Bergemann, Simon W. Campbell, Luca Casagrande, Richard de Grijs, Gayandhi De Silva, Maria Lugaro, Daniel B. Zucker, Angela Bragaglia, Diane Feuillet, Giuliana Fiorentino, Brian Chaboyer, Massimo Dall’Ora, Massimo Marengo, Clara E. Martínez-Vázquez, Noriyuki Matsunaga, Matteo Monelli, Joseph P. Mullen, David Nataf, Maria Tantalo, Frederic Thevenin, Fabio R. Vitello, Rolf Peter Kudritzki, Joss Bland-Hawthorn, Sven Buder, Ken Freeman, Janez Kos, Geraint F. Lewis, Karin Lind, Sarah Martell, Sanjib Sharma, Dennis Stello, Tomaž Zwitter

Abstrakt

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.

Organisation(en)

Institut für Astrophysik

Externe Organisation(en)

Università degli Studi di Roma "Tor Vergata", INAF - Osservatorio Astronomico di Padova, Monash University, ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Max-Planck-Institut für Astronomie, INAF - Osservatorio Astronomico di Roma, Space Science Data Center (SSDC) - Agenzia Spaziale Italiana (ASI), University of Texas, Austin, Instituto Nazionale die Astrofisica (INAF), Université Libre de Bruxelles, Australian National University, Macquarie University, International Space Science Institute - Beijing, MTA Társadalomtudományi Kutatóközpont, Magyar Tudományos Akadémia, Eötvös Loránd University Budapest, Lund Observatory, Dartmouth College, INAF-Osservatorio Astronomico di Capodimonte, Florida State University, Gemini Observatory Northern Operations Center, University of Tokyo, Kyoto Sangyo University, Instituto de Astrofísica de Canarias (IAC), Universidad de La Laguna, Iowa State University, Johns Hopkins University Krieger School of Arts and Sciences, Université Côte d'Azur, University of Hawaii, Ludwig-Maximilians-Universität München, The University of Sydney, University of Ljubljana, Stockholm University, University of New South Wales

Journal

Monthly Notices of the Royal Astronomical Society

Band

531

Seiten

137-162

Anzahl der Seiten

26

ISSN

0035-8711

DOI

https://doi.org/10.1093/mnras/stae1149

Publikationsdatum

06-2024

Peer-reviewed

Ja

ÖFOS 2012

103003 Astronomie, 103004 Astrophysik

Schlagwörter

ASJC Scopus Sachgebiete

Astronomy and Astrophysics, Space and Planetary Science

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/b45cd60f-58c3-48ef-b330-60291c67e935