Optical and ultraviolet observations of the X-ray globular cluster BO 158 in M31

Abstract

It is pointed out that the study of the globular cluster system in a galaxy is very important for understanding the formation, dynamics, and chemical evolution of that galaxy. The present investigation represents an attempt to determine the population content of the globular cluster Bo 158 in M31 through the analysis of its energy distribution in the visible and UV wavelength regions. The results are compared with the Galactic globular clusters for which analogous data are available. On the basis of the findings in the investigation it is concluded that Bo 158 in M31 shows characteristics of an EB-type cluster from the UV data, while the optical integrated photometry and spectroscopy would rather classify it as a relatively red metal-rich cluster. With allowance for the observational errors associated with the data, this discrepancy can be explained most likely by assuming that the 'second parameter' problem involved in the classification of globular clusters exists in M31 as well.