Probing galactic double-mode RR Lyrae stars against Gaia EDR3

Abstract

Context. Classical double-mode pulsators (RR Lyrae stars and δ Cepheids) are important because of their simultaneous pulsation in low-order radial modes. This enables us to place stringent constraints on their physical parameters. Aims. We use 30 bright galactic double-mode RR Lyrae (RRd) stars to estimate their luminosities and compare these luminosities with those derived from the parallaxes of the recent data release (EDR3) of the Gaia survey. Methods. We employed pulsation and evolutionary models together with observationally determined effective temperatures to derive the basic stellar parameters. Results. When we exclude six outlying stars (e.g., those with blending issues), the RRd and Gaia luminosities correlate well. With the adopted temperature zeropoint from one of the works based on the infrared flux method, we find it necessary to increase the Gaia parallaxes by 0.02 mas to bring the RRd and Gaia luminosities into agreement. This value is consonant with those derived from studies on binary stars in the context of Gaia. We also examined the resulting period-luminosity-metallicity (PLZ) relation in the 2MASS K band as follows from the RRd parameters. This leads to the verification of two independently derived other PLZs. No significant zeropoint differences are found. Furthermore, the predicted K absolute magnitudes agree within σ = 0.005 − 0.01 mag.

Theoretical Stellar Pulsation Physics

“…Among the most recent results obtained from this kind of pulsation modeling, we can quote the prediction of Cepheid instability strip boundaries and period-age relations as a function of both metallicity and the efficiency of rotation, by Anderson et al (2016). More recently, interesting results for the prediction of double mode RR Lyrae periods and period ratios have been obtained by Kovacs & Karamiqucham (2021) on the basis of their extensive sets of linear nonadiabatic models. In nonlinear convective hydrodynamical 1D models the hydrodynamic equations describing the pulsation phenomenon are not linearized, so that not only the periods and the instability strip edges but also the pulsation amplitudes (full amplitude variation of all the relevant quantities along the pulsation cycle) can be predicted.…”

On the use of field RR Lyrae as galactic probes – VI. Mixed mode RR Lyrae variables in Fornax and in nearby dwarf galaxies

“…In this context it is worth mentioning that, with a few exceptions (Kovacs & Karamiqucham 2021, and references therein), we still lack a dynamical mass measurement of an old, low-mass star during central helium burning phase (Horizontal Branch, HB), and in particular of RRLs. The exceptions are a few double-mode RRLs (RRd), i.e., RRLs pulsating simultaneously in the Fundamental (F) and in the First-overtone (FO) mode.…”