- ID:
- ivo://CDS.VizieR/J/AJ/108/1350
- Title:
- Omega Cen FUV photometry
- Short Name:
- J/AJ/108/1350
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We 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{AA} 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_{sun}_.
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- ID:
- ivo://CDS.VizieR/J/AJ/112/601
- Title:
- UV photometry in M79
- Short Name:
- J/AJ/112/601
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ultraviolet photometry is presented for the globular cluster M79 (NGC 1904) according to the final calibration of the images obtained on the Astro-1 Spacelab mission by the Ultraviolet Imaging Telescope. These results include both point-source and surface photometry at 152nm and 249nm. An ultraviolet color-magnitude (C-M) diagram in these bandpasses is presented. The detected stars are also cross-matched with the ground-based photometry of Ferraro et al. (1992MNRAS.256..391F) to produce C-M and two-color diagrams covering a 4000A span in wavelength. The observed horizontal branch (HB) is compared with stellar interior models of the zero-age HB (ZAHB). Many stars are found in post-HB evolutionary stages more luminous than the ZAHB. The distribution of stars along the ZAHB in m152-m249 color is investigated, and an indication of possible bimodality is found. The relative population of the blue HB tail may vary with radius for radii greater than 1'. Ultraviolet surface brightness and color-index profiles are presented. The previously reported central gradient in the m152-V color index is confirmed, and a faint diffuse component is detected outside a radius of 40" in the 152nm band. Two possible causes of the central color gradient are discussed: mass segregation, and the destruction of red giant envelopes by enhanced mass loss in the cluster core.
