Observations of the Ultraviolet-Bright Star in 47 Tucanae with the Hopkins Ultraviolet Telescope

Details Observations of the Ultraviolet-Bright Star in 47 Tucanae with the Hopkins Ultraviolet Telescope Observations of the Ultraviolet-Bright Star in 47 Tucanae with the Hopkins Ultraviolet Telescope

Nov 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...454l..47d&link_type=abstract

Astrophysical Journal Letters v.454, p.L47

Astronomy and Astrophysics

Astronomy

12

Galaxy: Globular Clusters: Individual Name: 47 Tucanae, Stars: Evolution, Stars: Individual Constellation Name: Bs 47 Tuscanae, Ultraviolet: Stars

Scientific paper

The ultraviolet-bright star "BS" in the globular cluster 47 Tuc (NGC 104) was observed with the Hopkins Ultraviolet Telescope (HUT) during the Astro-2 Space Shuttle mission in 1995 March. The resulting spectrum extends from 912 to 1840 A with a resolution of about 3 A. It has numerous absorption features, but no emission features other than terrestrial airglow lines. We have fitted the data with Kurucz stellar atmosphere models using a chi 2 minimization technique. The Kurucz model that best fits the observed spectrum has Teff = 11,000 K, log g = 2.5, and [M/H] = -1.0; however, it overpredicts the flux in the sub-Ly beta region by nearly a factor of 3. Kurucz line profiles fitted to the star's H delta Balmer line yield log g = 2.0. Assuming a distance of 4.6 +/- 1.0 kpc, we estimate the stellar luminosity to be log L/L&sun; = 3.07 +/- 0.20. These atmospheric parameters place the star on the Schonberner post--asymptotic giant branch (AGB) evolutionary tracks. We measure the equivalent widths of the star's absorption lines and find them consistent with the abundances of cluster giant-branch and AGB stars. We conclude that BS in 47 Tuc is a cluster member and that non-LTE effects and nonsolar abundance ratios not included in the Kurucz models are important in this star.

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