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We have analyzed FUSE, COS, GHRS, and Keck HIRES spectra of the UV-brightstar Barnard 29 in M13 (NGC 6205). By comparing the photospheric abundancesderived from multiple ionization states of C, N, O, Si, and S, we infer aneffective temperature T_eff = 21,400 +/- 400 K. Balmer-line fits yield asurface gravity log g = 3.10 +/- 0.03. We derive photospheric abundances of He,C, N, O, Mg, Al, Si, P, S, Cl, Ar, Ti, Cr, Fe, Ni, and Ge. Barnard 29 exhibitsan abundance pattern typical of the first-generation stars in M13, enhanced inoxygen and depleted in aluminum. An underabundance of C and an overabundance ofN suggest that the star experienced nonconvective mixing on the RGB. We see noevidence of significant chemical evolution since the star left the RGB; inparticular, it did not undergo third dredge-up. Previous workers found that thestar's FUV spectra yield an iron abundance about 0.5 dex lower than its opticalspectrum, but the iron abundances derived from all of our spectra areconsistent with the cluster value. We attribute this difference to our use ofmodel atmospheres without microturbulence, which is ruled out by careful fitsto optical absorption features. We derive a mass M_*/M_sun = 0.45 - 0.55 andluminosity log (L_*/L_sun) = 3.26 - 3.35. Comparison with stellar-evolutionmodels suggests that Barnard 29 evolved from a ZAHB star of mass M_*/M_sunbetween 0.50 and 0.55, near the boundary between the extreme and bluehorizontal branches.

Observations of the Ultraviolet-Bright Star Barnard 29 in the Globular Cluster M13 (NGC 6205)