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 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