Ultraviolet and optical observations of two stars belonging to the blue horizontal branch of the globular cluster M 15.

Abstract

Two stars belonging to the blue horizontal branch of the globular cluster M 15 have been observed in the ultraviolet with lUE and measurements have been made of their U B and V magnitudes. Measurements have also been made of B and V magnitudes for all the other stars which were in the JUE aperture and which are resolved in optical observations. Comparison of the observed optical and ultraviolet fluxes with fluxes computed from models gives effective temperatures of 17 500 ± 1000K for the two stars of the blue horizontal branch.