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Double-mode RR Lyrae star — robust distance and metallicity indicators

Published online by Cambridge University Press:  06 February 2024

Shu Wang*
Affiliation:
CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China Department of Astronomy, China West Normal University, Nanchong, 637009, China
Xiaodian Chen
Affiliation:
CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China School of Astronomy and Space Science, University of the Chinese Academy of Sciences, Beijing, 100049, China Department of Astronomy, China West Normal University, Nanchong, 637009, China
Jianxing Zhang
Affiliation:
CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China School of Astronomy and Space Science, University of the Chinese Academy of Sciences, Beijing, 100049, China
Licai Deng
Affiliation:
CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China School of Astronomy and Space Science, University of the Chinese Academy of Sciences, Beijing, 100049, China Department of Astronomy, China West Normal University, Nanchong, 637009, China

Abstract

RR Lyrae (RR Lyr) stars are a well-known and useful distance indicator for old stellar populations such as globular clusters and dwarf galaxies. Fundamental-mode RR Lyr (RRab) stars are commonly used to measure distances, and the accuracy of the determined distance is strongly constrained by metallicity. Here, we investigate the metallicity dependence in the period–luminosity (PL) relation of double-mode RR Lyr (RRd) stars. We find and establish a linear relation between metallicity and period or period ratio for RRd stars. This relation can predict the metallicity as accurately as the low-resolution spectra. Based on this relation, we establish a metallicity-independent PL relation for RRd stars. Combining the distance of the Large Magellanic Cloud and Gaia parallaxes, we calibrate the zero point of the derived PL relation to an error of 0.022 mag. Using RRd stars, we measure the distances of globular clusters and dwarf galaxies with an accuracy of 2-3% and 1-2%, respectively. In the future, RRd stars could anchor galaxy distances to an accuracy of 1.0% and become an independent distance ladder in the Local Group.

Type
Contributed Paper
Copyright
© The Author(s), 2024. Published by Cambridge University Press on behalf of International Astronomical Union

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