  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.
