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arXiv · 2605.28497

Spectroscopic metallicities and first α-element abundances of RR Lyrae stars in Baade's Window

J. Olivares Carvajal·Á. Rojas-Arriagada·M. Zoccali·B. Acosta-Tripailao·M. De Leo·R. Albarracín·M. Sanchez-Benavente·E. Valenti·G. Bono·S. Duffau·L. Sbordone·M. Fabrizio·V. F. Braga
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Abstract

RR Lyrae stars in the bulge have been reported to be associated with the spheroidal, relatively metal-poor component. They offer a way to trace this component with precise distances. While a few studies of RR Lyrae spectra with medium/high resolution are now available, none of them target stars in the Galactic bulge. We present here a spectroscopic determination of Fe and α-element abundances for RR Lyrae stars in the Galactic bulge, with the main goal of providing a benchmark to calibrate other metallicity indicators, appropriate for this specific stellar population. We analyzed FLAMES/GIRAFEE spectra of 78 RR Lyrae stars (60 ab-type and 18 c-type). We applied a full-spectrum fitting technique to obtain the spectroscopic metallicity and overall α-element abundance. Distances are derived by means of a period-luminosity-metallicity relation, and orbits are computed by combining the radial velocities derived here with the proper motions from DR3. Gaia The resulting metallicities peak at [Fe/H] _median = -1.34 +- 0.04 and -1.44 +- 0.08 dex for ab and c-types respectively. The majority of the bulge RR Lyrae are metal-poor stars with relatively high α-element abundances around [α/Fe] ~ 0.25 +- 0.03 dex. We used our spectroscopic measurements to test different methods for deriving metallicities based on photometry, which utilize Fourier parameters in the light curves of the RR Lyrae. The data suggest a possible correlation between the metallicity difference and the [α/Fe] ratio, which needs to be investigated further. There are some ab-type RR Lyrae that show metallicities higher than -1 dex and low [α/Fe] values. We studied these stars kinematically and found a difference between three stars with similar [α/Fe] values and the main group, indicating that they may be slightly younger and correspond to the disk population.

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J. Olivares Carvajal, Á. Rojas-Arriagada, M. Zoccali, B. Acosta-Tripailao, M. De Leo, R. Albarracín, M. Sanchez-Benavente, E. Valenti, G. Bono, S. Duffau, L. Sbordone, M. Fabrizio, V. F. Braga. 2026-05-27. Spectroscopic metallicities and first α-element abundances of RR Lyrae stars in Baade's Window. https://arxiv.org/abs/2605.28497

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