The elderly among the oldest: new evidence for extremely metal-poor RR Lyrae stars

We performed a detailed spectroscopic analysis of three extremely metal-poor RR Lyrae stars, exploring uncharted territories at these low metallicities for this class of stars. Using high-resolution spectra acquired with HARPS-N at TNG, UVES at VLT, and PEPSI at LBT, and employing Non-Local Thermodynamic Equilibrium (NLTE) spectral synthesis calculations, we provide abundance measurements for Fe, Al, Mg, Ca, Ti, Mn, and Sr. Our findings indicate that the stars have metallicities of [Fe/H] = −3.40 ± 0.05, −3.28 ± 0.02, and −2.77 ± 0.05 for HD 331986, DO Hya, and BPS CS 30317-056, respectively. Additionally, we derived their kinematic and dynamical properties to gain insights into their origins. Interestingly, the kinematics of one star (HD 331986) is consistent with the Galactic disc, while the others exhibit Galactic halo kinematics, albeit with distinct chemical signatures. We compared the [Al/Fe] and [Mg/Mn] ratios of the current targets with recent literature estimates to determine whether these stars were either accreted or formed in situ, finding that the adopted chemical diagnostics are ineffective at low metallicities ([Fe/H] ≲ −1.5). Finally, the established horizontal branch evolutionary models, indicating that these stars arrive at hotter temperatures on the Zero-Age Horizontal Branch (ZAHB) and then transition into RR Lyrae stars as they evolve, fully support the existence of such low-metallicity RR Lyrae stars. As a consequence, we can anticipate detecting more of them when larger samples of spectra become available from upcoming extensive observational campaigns.

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Publication Details

Journal
Astronomy and Astrophysics
Published
2025-01-10
DOI
https://doi.org/10.1051/0004-6361/202453202
Citations
4
Primary Topic
Astro and Planetary Science
Type
article
Field-Weighted Citation Impact
4.62

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The elderly among the oldest: new evidence for extremely metal-poor RR Lyrae stars

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The elderly among the oldest: new evidence for extremely metal-poor RR Lyrae stars

M. Monelli, M. Marconi, Sven Buder, Federico Sestito, Masaki Takayama, V. F. Braga, V. D’Orazi, G. Fiorentino, Alexey Bobrick, Joseph P. Mullen, V. Testa, C. Sneden, M. Fabrizio, Noriyuki Matsunaga, A. Pietrinferni, M. Sánchez-Benavente, M. Marengo, Nicholas Storm, J. Crestani, G. Bono, F. Cusano, Giuseppe Di Iorio, o
article en
4 citations

Abstract

We performed a detailed spectroscopic analysis of three extremely metal-poor RR Lyrae stars, exploring uncharted territories at these low metallicities for this class of stars. Using high-resolution spectra acquired with HARPS-N at TNG, UVES at VLT, and PEPSI at LBT, and employing Non-Local Thermodynamic Equilibrium (NLTE) spectral synthesis calculations, we provide abundance measurements for Fe, Al, Mg, Ca, Ti, Mn, and Sr. Our findings indicate that the stars have metallicities of [Fe/H] = −3.40 ± 0.05, −3.28 ± 0.02, and −2.77 ± 0.05 for HD 331986, DO Hya, and BPS CS 30317-056, respectively. Additionally, we derived their kinematic and dynamical properties to gain insights into their origins. Interestingly, the kinematics of one star (HD 331986) is consistent with the Galactic disc, while the others exhibit Galactic halo kinematics, albeit with distinct chemical signatures. We compared the [Al/Fe] and [Mg/Mn] ratios of the current targets with recent literature estimates to determine whether these stars were either accreted or formed in situ, finding that the adopted chemical diagnostics are ineffective at low metallicities ([Fe/H] ≲ −1.5). Finally, the established horizontal branch evolutionary models, indicating that these stars arrive at hotter temperatures on the Zero-Age Horizontal Branch (ZAHB) and then transition into RR Lyrae stars as they evolve, fully support the existence of such low-metallicity RR Lyrae stars. As a consequence, we can anticipate detecting more of them when larger samples of spectra become available from upcoming extensive observational campaigns.

Astronomy and AstrophysicsVol. 694
Florida State University (US), University of Rome Tor Vergata (IT), Australian National University (AU), University of Hertfordshire (GB), Universidad de La Laguna (ES), Kyoto Sangyo University (JP), Technion – Israel Institute of Technology (IL), University of Hyogo (JP), Malmö University (SE), Vanderbilt University (US), Astronomical Observatory of Rome (IT), Astronomical Observatory of Capodimonte (IT), Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna (IT), ASTRO-3D (AU), Gemini North Observatory (US), Max Planck Institute for Astronomy (DE), Collurania Teramo Observatory (IT), Instituto de Astrofísica de Canarias (ES), ARC Centre of Excellence for All-sky Astrophysics (AU), Osservatorio Astronomico di Padova (IT), Universitat de Barcelona (ES), The University of Tokyo (JP), The University of Texas at Austin (US), National Institute for Astrophysics (IT)
National Science Foundation, European Commission, Deutsche Forschungsgemeinschaft, Ministerio de Ciencia e Innovación, Fundación Bancaria Caixa d'Estalvis i Pensions de Barcelona, Instituto de Astrofísica de Canarias, Science and Technology Facilities Council, European Regional Development Fund, Agencia Estatal de Investigación
Openalex Percentile: Top 7%
Astro and Planetary Science
4.62
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