Masses of RR Lyrae Stars with Different Chemical Abundances in the Galactic Field

Abstract

The surface gravities and effective temperatures have been added to a compilative catalog published earlier, which includes the relative abundances of several chemical elements for 100 field RR Lyrae stars. These atmoshperic parameters and evolutionary tracks from the Dartmouth database are used to determine the masses of the stars and perform a comparative analysis of the properties of RR Lyrae stars with different chemical compositions. The masses of metal-rich ($\rm{[Fe/H]}> -0.5$) RR Lyrae stars with thin disk kinematics are in the range $(0.51-0.60)M_{\odot}$. Only stars with initial masses exceeding $1M_{\odot}$ can reach the horizontal branch during the life time of this subsystem. To become an RR Lyrae variable, a star must have lost approximately half of its mass during the red-giant phase. The appearance of such young, metal-rich RR Lyrae stars is possibly due to high initial helium abundances of their progenitors. According to the Dartmouth evolutionary tracks for Y = 0.4, a star with an initial mass as low as $0.8M_{\odot}$ could evolve to become an RR~Lyrae variable during this time. Such stars should have lost $(0.2-0.3)M_{\odot}$ in the red-giant phase, which seems quite realistic.