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[47.12] The Most Luminous Hot Stars of NGC 604

C.L. Miskey, F.C. Bruhweiler, M. Smith Neubig (IACS/CUA)

Using the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope (HST), we observed NGC 604, the extraordinarily bright H II, star-forming region located in the spiral galaxy M33. Our observational objective was to obtain ultraviolet spectra of a large number of OB stars from a single image. The 1720 second exposure was taken with the FUV-MAMA detector, G140L grating, and 52"x2" aperture. The 2-D spectral image contains at least 40 UV stellar spectra spanning the wavelength range 1150 to 1730Å. By utilizing the unique capabilities of STIS and our new data reduction scheme, we have isolated the spectra of seven stars thus far with S/N sufficient to deduce detailed spectral properties. These stars are the hottest, most luminous stars of NGC 604. We have determined the positions of these stars in the H-R diagram using the UV spectral diagnostics previously developed by Neubig & Bruhweiler and derived photometry from previous HST imagery. The UV spectral types are O4-B0 and indicate very young stars (ages < 4 Myr). The most luminous star has a spectral type of O5 and a M_bol near -11.8. In addition to pronounced mass loss profiles for N V, Si IV, and C IV, these stars typically show strong emission from He II 1640Å. So far, we have identified two Wolf-Rayet stars based upon their UV spectra. The prominent He II emission and the strength of the stellar photospheric spectrum suggest a metallicity close to that of the Milky Way. Further STIS observations and analyses are underway of other OB associations in the Local Group galaxies. We acknowledge support from NASA grant NAG5-3378 to CUA.