Far Ultraviolet Photometry of Globular Clusters

Details Far Ultraviolet Photometry of Globular Clusters Far Ultraviolet Photometry of Globular Clusters

Dec 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aas...18511601w&link_type=abstract

American Astronomical Society, 185th AAS Meeting, #115.05; Bulletin of the American Astronomical Society, Vol. 26, p.1513

Astronomy and Astrophysics

Astronomy

Scientific paper

Far-Ultraviolet exposures (centroid 1620 Angstroms; bandwidth 225 Angstroms; field of view 40 arcmin) were obtained of the globular clusters omega Cen (NGC 5139), M3 (NGC 5272), and M13 (NGC 6205) with the Ultraviolet Imaging Telescope (UIT) during the Astro-1 mission of December 1990. The 291 sec exposure of omega Cen extends to a far-ultraviolet (FUV) magnitude of 16.4, providing a complete sample of 1957 hot horizontal branch (HB) and supra-HB stars even into the dense core of the cluster. The far-UV observations of omega Cen were combined with Stromgren u CCD observations from CTIO to produce a FUV, u color-magnitude diagram. The CMD permits analysis of the HB structure, showing a large population of supra-HB stars, a thickly populated extreme HB, and a discontinuity at Te = 16000K. The 199 sec exposure of M3 extends to a FUV magnitude of 16.2, sufficient to detect the hottest HB stars and all the hot supra-HB stars. Over 70 sources are detected. The 46 sec exposure of M13 provides photometry for over 40 stars, most of them supra-HB objects, as the FUV magnitude limit is approximately 14.2, slightly above the expected FUV magnitude of the HB. Compared to the most comprehensive grid of HB and post-HB evolutionary models (Dorman et al. 1993, ApJ, 419, 596), the observed numbers of supra-HB stars appear consistent with the evolution of hot HB stars into supra-HB stars. The clusters with bluer HB morphology (omega Cen, M13) produce proportionally more supra-HB stars than the cluster without the blue morphology (M3).

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