The Oosterhoff Dichotomy in the Globular Cluster ω Centauri

Details The Oosterhoff Dichotomy in the Globular Cluster ω Centauri The Oosterhoff Dichotomy in the Globular Cluster ω Centauri

May 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000aas...196.4103c&link_type=abstract

American Astronomical Society, 196th AAS Meeting, #41.03; Bulletin of the American Astronomical Society, Vol. 32, p.739

Astronomy and Astrophysics

Astronomy

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Scientific paper

The population of RR Lyrae variables in ω Centauri includes stars of both Oosterhoff types. Consequently, these stars provide a good data set for testing theories of horizontal branch evolution. In the present study, we analyse the V magnitudes published by Kaluzny et al. (1997, A&AS, 125, 343) for the RRc variables. Our approach is to calculate the masses and luminosities using equations that Simon & Clement (1993, ApJ, 410, 526) derived from Fourier decomposition of light curves based on hydrodynamic RRc pulsation models. The calculated luminosities correlate well with the mean V magnitudes, indicating that the equations of Simon & Clement seem to be valid. The variables are assigned an Oosterhoff class according to their position in the period-amplitude plane and we find that the Oosterhoff type II (OoII) stars are more luminous than the OoI stars. However, the mean mass derived for the OoII RRc stars is lower than that of the OoI stars: 0.53 {Msun} for OoII compared with 0.59 {Msun} for OoI. These results support the Lee, Demarque & Zinn (1990, ApJ, 350, 155) hypothesis that the RR Lyrae variables in Oosterhoff type I clusters are ZAHB stars while those in the OoII clusters are brighter, lower mass stars that have evolved from the BHB. This research has been supported by the Natural Sciences and Engineering Research Council of Canada.

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