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arXiv · 2411.02514

The Dog that Didn't Bark: Non-Variable Field Stars in the RR Lyrae Instability Strip

Yuxi Lu·Cecilia Mateu·K. Z. Stanek
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Abstract

RR Lyrae stars (RRLs) are easy to identify thanks to their large photometric variation and short periods. All stars in the RRL instability strip are pulsators is often a hidden assumption in most stellar population studies using RRLs. Non-variable stars in the instability strip have been discovered for Cepheids and $\delta$ Scuti, and in this paper, we report the discovery of non-variable filed stars in the RRL instability strip. Using a high-quality sample selected from Gaia DR3, we find at least 15% of the stars in the empirical instability strip where the variable fraction is > 0.7 have near-zero photometric variations or variations that are significantly smaller than typical RRLs. The non-variable stars are mostly bright and close by, on cold orbits in the Galactic plane. Metallicity from Gaia BP/RP spectra suggests the non-variable stars have an average metallicity is ~ -0.5 dex, with a peak at 0. The discovery of these non-variable stars in the RRL instability strip challenges our understanding of stellar physics and further investigation is needed to understand the origin of these stars.

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Yuxi Lu, Cecilia Mateu, K. Z. Stanek. 2024-11-04. The Dog that Didn't Bark: Non-Variable Field Stars in the RR Lyrae Instability Strip. https://arxiv.org/abs/2411.02514

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