UIT - ULTRAVIOLET OBSERVATIONS OF THE SMALL MAGELLANIC CLOUD

A mosaic of four UIT far-UV (FUV) (lambda(eff)=1620 Angstrom) images, with derived stellar and H II region photometry, is presented for most of the Bar of the SMC. The UV morphology of the SMC's Bar shows that recent star formation there has left striking features including: (a) four concentrations of UV-bright stars spread from northeast to southw est at nearly equal (similar to 30 arcmin=0.5 kpc) spacings; (b) one o f the concentrations, near DEM 55, comprises a well-defined 8-arcmin d iameter ring surrounded by a larger H alpha ring, suggestive of sequen tial star formation. FUV PSF photometry is obtained for 11,306 stars i n the FUV images, resulting in magnitudes m(162). We present a FUV lum inosity function for the SMC Bar, complete to m(162)similar to 14.5. D etected objects are well correlated with other SMC Population I materi al; of 711 H alpha emission-line stars and small nebulae within the UI T fields of view, 520 are identified with FUV sources. The FUV photome try is compared with available ground-based catalogs of supergiants, y ielding 191 detections of 195 supergiants with spectral type earlier t han F0 in the UIT fields. The (m(162)-V) color for supergiants is a se nsitive measure of spectral type. The bluest observed colors for each type agree well with colors computed from unreddened Galactic spectral atlas stars for types earlier than about A0; for later spectral types the observed SMC stars range significantly bluer, as predicted by com parison of low-metallicity and Galactic-composition models. Redder col ors for some stars of all spectral types are attributed to the strong FUV extinction arising from even small amounts of SMC dust. Internal S MC reddenings are determined for all catalog stars. All stars with E(B -V)>0.15 are within regions of visible H alpha emission. FUV photometr y for 42 H alpha-selected H II regions in the SMC Bar is obtained for stars and for total emission (as measured in H II-region-sized apertur es). The flux-weighted average ratio of total to stellar FUV flux is 2 .15; consideration of the stellar FUV luminosity function indicates th at most of the excess total flux is due to scattered FUV radiation, ra ther than stars fainter than m(162)=14.5. Both stellar and total emiss ion are well correlated with H alpha fluxes measured by Kennicutt and Hodge [ApJ. 306, 130 (1986)], yielding FUV/H alpha flux ratios that ar e consistent with models of SMC metallicity, ages from 1-5 Myr, and mo derate (E(B-V) = 0.0-0.1 mag) internal SMC extinction. (C) 1997 Americ an Astronomical Society.