The Nature of Young RR Lyrae Field Stars with Solar Metallicity.

Based on published parameters of their atmospheres, the masses of 100 RR Lyrae variables (lyrids) in the field are determined using evolutionary tracks from the Dartmouth data base and the properties of lyrids with different metallicities are compared. It was found that the masses of the metal-rich ([Fe/H] > –0.5) lyrids with thin-disk kinematics lie within an interval of (0.51-0.60) Mʘ. According to modern concepts, the initial masses of these stars should be no more than (0.7-0.8) Mʘ. The long evolution time of these low-mass stars conflicts with the significantly lower age of even the oldest stars in the thin-disk subsystem of the Galaxy. A possible explanation is proposed for the nature of these comparatively young and metal-rich variables. [ABSTRACT FROM AUTHOR]