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 ( [ 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 1 M _ { \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 0.8 M _ { \odot } could evolve to become an RRÂ 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 .
Populations of red giants and RR Lyrae stars with such high helium abundances have already been discovered in the bulge ; some of these could easily be transported to the solar neighborhood as a consequence of perturbations due to inhomogeneities of the Galaxy’s gravitational potential .