IUE observations of blue horizontal branch stars in the globular clusters M 3 and NGC 6752

Abstract

IUE observations of 3 blue horizontal branch (BHB) stars in M 3 and 4 stars in NGC 6752 are presented. In addition, unpublished IUE archive data have been used for 5 more BHB stars in NGC 6752. Using the most recent model atmospheres (Kurucz 1992) the physical parameters of these stars have been derived, and compared with the ZAHB evolutionary tracks by Dorman et al. (1993). All the stars, including those that appear to be evolved off the ZAHB, are consistent with the theoretical predictions. The present results are compared with those obtained in previous similar analyses: the possible presence of some low-gravity stars is confirmed in M 3, while no clear indication is found of multiple stellar populations on the HB of NGC 6752. However different populations, if any, would be difficult to identify in the logg-logT_e_ plane because of the simultaneous effect of various parameters and the poor accuracy of the gravity estimates from IUE data.