The Metallicities and Kinematics of RR Lyrae Variables III. On the Production of Metal-Rich RR Lyrae Stars

Details The Metallicities and Kinematics of RR Lyrae Variables III. On the Production of Metal-Rich RR Lyrae Stars The Metallicities and Kinematics of RR Lyrae Variables III. On the Production of Metal-Rich RR Lyrae Stars

Nov 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aj....110.2312l&link_type=abstract

Astronomical Journal v.110, p.2312

Astronomy and Astrophysics

Astronomy

24

Stars: Abundances, Stars: Variables: Rr Lyrae

Scientific paper

Using the densities and space distributions of local RR Lyrae stars and their progenitors, we estimate the efficiency of RR Lyrae production for the old thin disk, the thick disk, and the metal-weak thick disk, relative to the halo. We find that RR Lyraes form from thick disk ([Fe/H]> -1.0) horizontal branch (HB) stars with about 1/40 the frequency that they form in the halo. The ratio is about 1/800 for the old thin disk, and about 1/25 for the metal-weak thick disk ([Fe/H] ≤ -1.0). The production efficiency increases with decreasing metal abundance, as if the bulk of the HB stars moves blueward toward the instability strip. In each of the three disk subpopulations, it appears that only the extreme tail of the HB star distribution reaches blueward into the instability strip. We find the formation efficiency of RR Lyraes in disk globular clusters to be about equal to that for the thick disk RR Lyraes of the field. That is, the small number of RR Lyrae stars observed in disk clusters, relative to field thick disk RR Lyraes, is largely due to the small number of progenitors available in the clusters, relative to the field within several kiloparsecs of the Sun. Some of the RR Lyrae stars in disk globular clusters appear to have anomalously long periods relative to field RR Lyraes of similar abundance. This may be related to the denser stellar environments of the clusters, and may be a red-HB manifestation of the extended blue HBs seen in many dense clusters at lower abundances.

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