Observations of the UV-Bright Star BS in 47 Tucanae\\ with the Hopkins Ultraviolet Telescope
Session 22 -- Stellar Spectroscopy, Atmospheres, Models, Intrinsic Variables, Theory, Part II
Display presentation, Tuesday, June 13, 1995, 9:20am - 6:30pm

## [22.15] Observations of the UV-Bright Star BS in 47 Tucanae\\ with the Hopkins Ultraviolet Telescope

W.V.Dixon, A.F.Davidsen (JHU), H.C.Ferguson (STScI)

The UV-bright star BS in the globular cluster 47 Tuc was observed with the Hopkins Ultraviolet Telescope (HUT) during the Astro-2 space shuttle mission in 1995 March. The resulting spectrum extends from the interstellar cutoff at 912 \AA\ to 1850 \AA\ with a resolution of $\sim$ 3 \AA. It shows numerous absorption features, but no significant emission features other than terrestrial airglow lines. Detailed fitting of Kurucz stellar atmosphere models using a $\chi^2$ minimization technique indicates $T_{eff} = 11,000$~K, $\log g = 2.5$, and $\log Z/Z_{\sun} = -1.0$. The Kurucz model which best fits the observed spectrum overpredicts the flux in the Lyman~$\gamma$ to Lyman~$\beta$ region by nearly a factor of three, suggesting that opacity effects not included in the models are important even at this relatively low temperature. Assuming a distance of $4.6 \pm 1.0$ kpc, we estimate the stellar luminosity to be $\log L/L_{\sun} = 3.1 \pm 0.2$. These atmospheric parameters place the star on the Sch\"onberner post-AGB evolutionary tracks.

The Hopkins Ultraviolet Telescope Project is supported by NASA contract NAS 5-27000 to The Johns Hopkins University.