Abstract
We report on the observations of nine globular clusters carried out by the Voyager ultraviolet spectrometers (UVSs). Three of the observed clusters, M13, NGC 6752, and M70, exhibit an intense far-ultraviolet (FUV) spectrum down to the Lyman limit. However, the spectrum obtained for NGC 6752 is heavily contaminated by the nearby star HD 177999 for wavelengths longward of 1200 A. For M70 the Voyager spectrum is completely dominated by the B3 star HD 172535. The FUV spectral energy distribution of M13 confirms results from the Ultraviolet Imaging Telescope that the main contributors to the FUV emission are hot sdB stars. M13's integrated spectrum resembles that of an sdB star of Teff ≈ 28,000 K. For two clusters, M92 and M5, UVS detected a weak signal, making it difficult to reach any conclusion on the underlying hot components of the systems. Four clusters, M15, NGC 2298, NGC 6656, and NGC 6793, were observed but not detected. In some cases it was possible to identify a weak stellar spectrum, which, however, very likely originates from foreground FUV emitters not related to the systems. For the nondetected clusters we provide upper limits on the FUV flux.
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