Astronomy and Astrophysics – Astronomy
Scientific paper
May 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aas...188.2802s&link_type=abstract
American Astronomical Society, 188th AAS Meeting, #28.02; Bulletin of the American Astronomical Society, Vol. 28, p.860
Astronomy and Astrophysics
Astronomy
Scientific paper
The nearby globular cluster NGC 6752 was observed with the Ultraviolet Imaging Telescope (UIT) during the Astro-2 Space Shuttle mission in 1995 March. We detect 348 hot horizontal branch (HB) star candidates on the image. This number should be nearly a complete census of the HB population because (1) the UIT field of view of 40' is well matched to the cluster diameter, (2) the solar-blind detectors on UIT suppress the cool star population, and minimize crowding effects even in the cluster core, and (3) the ground-based color-magnitude diagram (CMD) of Buonanno et al. (1986) shows that the HB contains only hot stars. We present an ultraviolet -- visible CMD for the 211 stars with ground-based photometry available from the Buonanno et al. catalog. The UIT absolute calibration is well-determined from comparison with 18 hot HB stars in the cluster observed with IUE. Four hot (Teff ~ 35,000 K) luminous (log L/Lsun = 2.1) stars in the CMD are plausibly identified as being directly descended off of the extreme horizontal branch (EHB). However, the large luminosity separation between these post-EHB stars and the EHB is not predicted by canonical models of HB and post-HB evolution. We show that this luminosity separation and the numbers of post-EHB stars can be explained by noncanonical models whose envelopes have been enriched in helium by internal mixing during the preceding red-giant-branch phase.
Bohlin Ralph Charles
Landsman Wayne B.
Neff Susan
O'Connell Robert West
Roberts Morton S.
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