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

D’Orazi, Valentina ; Storm, Nicholas ; Casey, Andrew R. ; Braga, Vittorio F. ; Zocchi, Alice ; Bono, Giuseppe ; Fabrizio, Michele ; Sneden, Christopher ; Massari, Davide and Giribaldi, Riano E. , et al. (2024) In Monthly Notices of the Royal Astronomical Society 531(1). p.137-162
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... (More)

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.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Galaxy: abundances, Galaxy: disc, Galaxy: halo, stars: abundances, stars: Population II, stars: variables: RR Lyrae
in
Monthly Notices of the Royal Astronomical Society
volume
531
issue
1
pages
26 pages
publisher
Oxford University Press
external identifiers
  • scopus:85193505328
ISSN
0035-8711
DOI
10.1093/mnras/stae1149
language
English
LU publication?
yes
id
495976fa-6ae5-4e8c-922a-28cb318e90e8
date added to LUP
2024-06-04 15:06:25
date last changed
2024-06-04 15:07:43
@article{495976fa-6ae5-4e8c-922a-28cb318e90e8,
  abstract     = {{<p>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.</p>}},
  author       = {{D’Orazi, Valentina and Storm, Nicholas and Casey, Andrew R. and Braga, Vittorio F. and Zocchi, Alice and Bono, Giuseppe and Fabrizio, Michele and Sneden, Christopher and Massari, Davide and Giribaldi, Riano E. and Bergemann, Maria and Campbell, Simon W. and Casagrande, Luca and de Grijs, Richard and De Silva, Gayandhi and Lugaro, Maria and Zucker, Daniel B. and Bragaglia, Angela and Feuillet, Diane and Fiorentino, Giuliana and Chaboyer, Brian and Dall’Ora, Massimo and Marengo, Massimo and Martínez-Vázquez, Clara E. and Matsunaga, Noriyuki and Monelli, Matteo and Mullen, Joseph P. and Nataf, David and Tantalo, Maria and Thevenin, Frederic and Vitello, Fabio R. and Kudritzki, Rolf Peter and Bland-Hawthorn, Joss and Buder, Sven and Freeman, Ken and Kos, Janez and Lewis, Geraint F. and Lind, Karin and Martell, Sarah and Sharma, Sanjib and Stello, Dennis and Zwitter, Tomaž}},
  issn         = {{0035-8711}},
  keywords     = {{Galaxy: abundances; Galaxy: disc; Galaxy: halo; stars: abundances; stars: Population II; stars: variables: RR Lyrae}},
  language     = {{eng}},
  month        = {{06}},
  number       = {{1}},
  pages        = {{137--162}},
  publisher    = {{Oxford University Press}},
  series       = {{Monthly Notices of the Royal Astronomical Society}},
  title        = {{The GALAH survey : tracing the Milky Way’s formation and evolution through RR Lyrae stars}},
  url          = {{http://dx.doi.org/10.1093/mnras/stae1149}},
  doi          = {{10.1093/mnras/stae1149}},
  volume       = {{531}},
  year         = {{2024}},
}