AAS 198th Meeting, June 2001
Session 42. Star Clusters
Display, Tuesday, June 5, 2001, 10:00am-6:30pm, Exhibit Hall

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[42.09] Mapping the Upper H-R Diagram of NGC 604 with the HST/STIS.

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

We present results of a study using previous HST photometry and our two-dimensional spectral image obtained with the HST Space Telescope Imaging Spectrograph for the ``starburst'' NGC 604 in the nearby Local Group galaxy M33. The HST/STIS data were acquired using the G140L grating and the MAMA detector, which provided a wavelength coverage spanning 1170-1730Å. From a single 1720s STIS exposure, we have derived individual UV spectral types for approximately 37 stars in the crowded stellar field within the 25" x 2" area sampled by the STIS aperture. These stars represent a significant fraction of the young O & B stars in NGC 604. Several stellar objects have pronounced emission from He II 1640Å, signaling either W-R stars or luminous O stars with strong emission. By combining UV fluxes with previous HST photometry at visual wavelengths, we present UV through visual photometry for at least 60 stars. Using a corresponding WFPC2 image, we present a map of the location of these individual stars in the STIS aperture. We have further used these data to determine absolute magnitudes and positions of these stars in upper H-R diagram for NGC 604. An age of 3 Myr is inferred for the most luminous O stars, where an older background population also seems to be present. We estimate the slope of the IMF in NGC 604 is comparable to that found near the Sun in our Galaxy.

We acknowledge support through NASA grant NAG5-3378 to CUA.

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