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Far-ultraviolet photometry of the globular cluster omega CenWe present far-ultraviolet images of the globular cluster omega Centauri obtained with the Ultraviolet Imaging Telescope (UIT) during the 1990 December Astro-1 mission. A total of 1957 sources are detected at 1620 A to a limiting ultraviolet (UV) magnitude of 16.4 in the central 24 min diameter region of the field and a limit of 15.6 over the remainder of the 40 min diameter field. Over 1400 of these sources are matched with stars on a Stroemgren u band charge coupled devices (CCD) frame obtained with the Cerro Tololo Inter-American Observatory (CTIO) 0.9 m telescope to produce a (far-UV, u) color-magnitude diagram (CMD). Completeness of the sample and error estimates are determined by photometry of artificial stars added to the images. The horizontal branch (HB) of the CMD is heavily populated hotter than 9000 K. A large number of 'extreme HB' stars are found hotter than a conspicuous break in the HB at T(sub e) approximately 16000 K. There is also a significant population of stars above the HB, the brightest of which is 4 mag brighter than the HB. Most of the hotter of these appear to be 'AGB-manque' or 'Post-Early Asymptotic Giant Branch' stars. We compare the observations to recent theoretical evolutionary tracks for the zero-age HB and subsequent phases. The tracks match the data well, with the exception of the hotter HB stars, many of which fall below the zero-age horizontal branch. It is unclear as yet whether these are a special population or an artifact of errors in the models or photometry. We identify 33 stars with T(sub e) greater than or approximately = 50000 K, which are hotter than zero-age HB stars with envelope masses of 0.003 solar mass.
Document ID
19950032388
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Whitney, Jonathan H.
(Univ. of Virginia, Charlottesville, VA United States)
O'Connell, Robert W.
(Univ. of Virginia, Charlottesville, VA United States)
Rood, Robert T.
(Univ. of Virginia, Charlottesville, VA United States)
Dorman, Ben
(Univ. of Virginia, Charlottesville, VA United States)
Landsman, Wayne B.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Cheng, K.-P.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Bohlin, Ralph C.
(Space Telescope Science Institute, Baltimore, MD United States)
Hintzen, Paul M. N.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Roberts, Morton S.
(National Radio Astronomy Observatory, Charlottesville, VA United States)
Smith, Andrew M.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 16, 2013
Publication Date
October 1, 1994
Publication Information
Publication: The Astronomical Journal
Volume: 108
Issue: 4
ISSN: 0004-6256
Subject Category
Astronomy
Accession Number
95A63987
Funding Number(s)
CONTRACT_GRANT: NAS5-700
CONTRACT_GRANT: NAGW-2596
Distribution Limits
Public
Copyright
Other

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