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J/AJ/108/1350       Omega Cen FUV photometry                 (Whitney+, 1994)

Far-ultraviolet photometry of the globular cluster Omega Cen. Whitney J.H., O'Connell R.W., Rood R.T., Dorman B., Landsman W.B., Cheng K.-P., Bohlin R.C., Hintzen P.M.N., Roberts M.S., Smith A.M., Smith E.P., Stecher T.P. <Astron. J. 108, 1350 (1994)> =1994AJ....108.1350W
ADC_Keywords: Clusters, globular ; Photometry, ultraviolet Mission_Name: UIT Abstract: We present far-ultraviolet images of the globular cluster ω Centauri obtained with the Ultraviolet Imaging Telescope (UIT) during the 1990 December Astro-1 mission. A total of 1957 sources are detected at 1620Å to a limiting UV magnitude of 16.4 in the central 24' diameter region of the field and a limit of 15.6 over the remainder of the 40' diameter field. Over 1400 of these sources are matched with stars on a Stroemgren u band CCD frame obtained with the CTIO 0.9m telescope to produce a (far-UV, u) color-magnitude diagram. 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 9000K. A large number of "extreme HB" stars are found hotter than a conspicuous break in the HB at Te∼16000K. There is also a significant population of stars above the HB, the brightest of which is 4mag 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 Te≳50000K, which are hotter than zero-age HB stars with envelope masses of 0.003M. Objects: ---------------------------------------------------------- RA (2000) DE Designation(s) ---------------------------------------------------------- 13 26 45.9 -47 28 37 omega Cen = NGC 5139 = HD 116790 ---------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table3.dat 65 144 Bright UV sources
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 4 I4 --- WOR Sequential number (1) 6- 12 F7.2 pix Dx Offset in x position (2) 14- 20 F7.2 pix Dy Offset in y position (2) 22- 26 F5.2 mag mFUV FUV magnitude, calibrated by IUE 28- 32 F5.2 mag m3500 ? 3500Å magnitude 34- 38 F5.2 pix dxu ? Offset of the Stroemgren u source position from the predicted centroid of the UIT source 40- 44 F5.2 pix dyu ? Offset of the Stroemgren u source position from the predicted centroid of the UIT source 46 I1 --- Q1 Quality flag on UV-Optical match (3) 47 I1 --- Q2 Quality flag on Optical image 48 I1 --- Q3 Quality flag on UV Image 50- 54 F5.2 mag Vmag ? Dickens et al. (1988) V magnitude (4) 56- 60 F5.2 mag B-V ? Dickens et al. (1988) B-V colour index (4) 62- 65 I4 --- NDi ? Dickens et al. (1988) number (4)
Note (1): Cl* NGC 5139 WOR NNNN in Simbad Note (2): Offsets from the cluster center, RA=13h26min58.23s, DE=-47°25'20.384" (J2000). To calculate approximate right ascension and declination in radian, see text. Dx increases to the West and Dy increases to the North Note (3): Quality flag descriptions: ----------------------------------------------------- Flag UV-Optical match Optical image UV Image ----------------------------------------------------- 1 Accurate Isolated Isolated 2 Likely Double Double 3 Questionable Multiple Multiple 4 Poor Faint/Noisy Faint noisy 5 NA Defect Defect ----------------------------------------------------- Note (4): Dickens et al., 1988, Rutherford Appleton Laboratory, RAL 88-04
History: Prepared via OCR at CDS.
(End) James Marcout, Patricia Bauer [CDS] 11-Mar-1999
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