Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aj....108.1325g&link_type=abstract
The Astronomical Journal, vol. 108, no. 4, p. 1325-1349
Astronomy and Astrophysics
Astronomy
43
Astronomical Photometry, Astronomical Spectroscopy, Cepheid Variables, Interstellar Extinction, Stellar Composition, Stellar Evolution, Stellar Luminosity, Stellar Spectra, Ultraviolet Astronomy, Ultraviolet Spectra, Abundance, Asymptotic Giant Branch Stars, Atmospheric Models, Charge Coupled Devices, H Beta Line, H Gamma Line, Spectrographs, Stellar Atmospheres, Stellar Models, Ultraviolet Spectroscopy
Scientific paper
Spectroscopic observations of ultraviolet (UV)-bright stars were acquired and analyzed in the framework of recent theories concerning post-horizontal branch stellar evolution. The abundances of 26 elements were calculated for 5 UV-bright stars in the omega Cen from high resolution charge coupled devices (CCD) spectra. In contrast to the giants, the most luminous UV-bright stars in omega Cen display significant enhancements of the CNO and s-process elements. Among the UV-bright stars, the CNO enhancements appear abruptly at about log L/L solar luminosity = 2.7. The CNO and s-process enhancements are correlated in general in omega Cen, implying that these two sets of elements are mixed into the atmosphere together. The CNO and s-process element abundances of the most luminous UV-bright stars are about 1 dex greater than those of the typical red giant in omega Cen. The UV-bright stars also show an apparent deficiency of Al; the most likely cause of this is mass loss combined with a small nonlocal thermodynamic equilibrium (NLTE) effect. An analysis of the s-process element abundances demonstrates that the average time integrated neutron flux, tau0, for the most luminous UV-bright stars in omega Cen, V1 and ROA 24, is about 0.6/mb. The amount of s-process element enhancement observed in V1 and ROA 24 requires that about 0.1% of their atmospheres be composed of material mixed to the surface from the s-processed region. The observed s-process abundance patterns are also consistent with theoretical thermally pulsing asymptotic giant branch (AGB) models.
Gonzalez Guillermo
Wallerstein George
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