UV-bright stars in galactic globular clusters, their far-UV spectra and their contribution to the globular cluster luminosity.

Abstract

Ultraviolet-bright stars in 7 galactic globular clusters have been observed with 4 - 7 Å spectral resolution between 1150 Å and 3200 Å. The UV-bright stars, which are in the post-AGB (PAGB) phase of evolution, have effective temperatures between 19,000 and 35,000K, and have luminosities of about 10^3.3L_sun;. They generate on average about 0.3% of the total cluster luminosity. The ionizing photons produced by UV-bright stars may be an essential factor for the ionization structure of gas in the Milky Way halo. The PAGB star spectra were dereddened with laws taking into account the regional differences in the Milky Way. Doing so, the earlier reported division of the UV-bluest clusters into an EB and B category is less pronounced.