AAS 196th Meeting, June 2000
Session 41. Globular Clusters
Display, Wednesday, June 7, 2000, 10:00am-7:00pm, Empire Hall South

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[41.03] The Oosterhoff Dichotomy in the Globular Cluster \omega Centauri

C.M. Clement, J.F. Rowe (Dept. of Astronomy, Univ. of Toronto)

The population of RR Lyrae variables in \omega 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 \it et al. \rm (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 {M\odot} for OoII compared with 0.59 {M\odot} 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.

The author(s) of this abstract have provided an email address for comments about the abstract: cclement@astro.utoronto.ca

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