STELLAR ABUNDANCES AND WINDS OF A-TYPE SUPERGIANT STARS IN M33 - FIRST RESULTS FROM THE KECK HIRES SPECTROGRAPH

In this Letter, we report the first results of detailed analyses of A- type supergiants in M33 from high-quality Keck HIRES echelle spectra. The two stars, designated 117-A and B-324, now constitute the most dis tant stars for which detailed abundances have been measured. We find 1 17-A is metal-poor (roughly 1/10 solar), resembling an early A supergi ant in the SMC. B-324 has P Cygni-like profiles for most of the metal lines, but fitting only the photospheric component yields metal abunda nces similar to solar. These two stars are located at distinctly diffe rent galactocentric distances in M33; comparing their abundances shows that the metallicity gradient of this galaxy, previously reported onl y from H II-region surveys, is also qualitatively apparent in these st ars. Estimates of the stellar-wind parameters for these stars yield ma ss-loss rates of similar to 2.5 x 10(-8) M. yr(-1) for 117-A and simil ar to 1.2 x 10(-5) Mo yr(-1) for B-324 from the H alpha line profiles. When we examine the location of these stars in the wind momentum-lumi nosity plane, we find that they are in excellent agreement with the lo ci of luminous blue stars in the Galaxy, LMC, and SMC, taking into acc ount differences in metallicity.