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The Bright Star in the globular cluster 47 Tucanae (NGC 104) is a post-AGBstar of spectral type B8 III. The ultraviolet spectra of late-B stars exhibit amyriad of absorption features, many due to species unobservable from theground. The Bright Star thus represents a unique window into the chemistry of47 Tuc. We have analyzed observations obtained with the Far UltravioletSpectroscopic Explorer (FUSE), the Cosmic Origins Spectrograph (COS) aboard theHubble Space Telescope, and the MIKE Spectrograph on the Magellan Telescope. Byfitting these data with synthetic spectra, we determine various stellarparameters (T_eff = 10,850 +/- 250 K, log g = 2.20 +/- 0.13) and thephotospheric abundances of 26 elements, including Ne, P, Cl, Ga, Pd, In, Sn,Hg, and Pb, which have not previously been published for this cluster.Abundances of intermediate-mass elements (Mg through Ga) generally scale withFe, while the heaviest elements (Pd through Pb) have roughly solar abundances.Its low C/O ratio indicates that the star did not undergo third dredge-up andsuggests that its heavy elements were made by a previous generation of stars.If so, this pattern should be present throughout the cluster, not just in thisstar. Stellar-evolution models suggest that the Bright Star is powered by aHe-burning shell, having left the AGB during or immediately after a thermalpulse. Its mass (0.54 +/- 0.16 M_sun) implies that single stars in 47 Tuc lose0.1--0.2 M_sun on the AGB, only slightly less than they lose on the RGB.

Observations of the Bright Star in the Globular Cluster 47 Tucanae (NGC 104)