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H. Yong, C. D. Bailyn, P. Demarque (Yale University)
Pulsations in sdB stars were predicted by Charpinet et al. (1996) and discovered observationally by Kilkenny et al. (1997). The theoretical models of Charpinet et al. suggest that the pulsation mechanism is enhanced with metallicity. Thus, the sdB stars in the metal rich open cluster NGC 6791 are good candidates for such pulsations. We present the results of CCD photometry taken at the WIYN Observatory of NGC 6791. Pulsations in the sdB star B5 are found with a period of about 101 sec. and an amplitude of 0.04 mag. in B. Both pulsation period and amplitude are consistent with previous observations of field sdB stars. This is the first detection of pulsations in a sdB star in a cluster environment. The detection of pulsations in sdB stars in a cluster gives us a unique opportunity to calculate physical properties of sdB stars (such as the core mass) through comparison with theoretical models. This may also give us the opportunity to independently determine the metallicity and initial helium content of NGC 6791.