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Session 82 - Globular Clusters.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center
We will present data on sdB stars in the globular clusters M 15, M 22, and NGC 6752. While NGC 6752 has been known to harbour sdBs for quite some time already (Heber et al., 1986), it has also been the only globular cluster known to do so. Only recently, sdB candidates in M 15 (Durrell amp; Harris, 1993) and in M 22 (Thejll, priv. comm) have been discovered. An analysis of one of the sdBs in M 15 was presented recently (Moehler, in press), while the data on the ones in M 22 will be shown at this meeting for the first time. The physical parameters of these stars (\teff\ and \logg ) are derived from optical and IUE spectrophotometric data, intermediate resolution spectroscopy and Strömgren photometry. Knowing the distances of the clusters we can also determine masses.
We want to compare the physical parameters of these stars for the different clusters to see what their evolutionary status is and how (or whether at all) it is affected by metallicity. We will also compare our findings to sdB stars found in the field of the Milky Way. In addition we want to see whether the problems encountered with the analyses of blue HB stars (Moehler et al., 1995) apply also to the sdB stars. These analyses showed the BHB stars to have significantly lower surface gravities and masses than predicted by theory. It turned out that this effect did not extend to the sdBs in NGC 6752 studied by Heber et al. (1986) which however constituted a sample too small to draw any meaningful conclusions.
Durrell P.R., Harris W.E., 1993, \aj1051420 Heber U., Kudritzki R.P., Caloi V., Castellani V., Danziger J., Gilmozzi \hspace*0.5cm R., 1986, \aua162171--179 Moehler S., Heber U., de Boer K.S., 1995, \aua29465 Moehler S., 1995, to appear in The Formation of the Galactic Halo - \hspace*0.5cm Inside and Out, Proceedings of the meeting at Tucson, Oct. 9-11, \hspace*0.5cm 1995, ASP Conf. Ser.
