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F. Bruhweiler (CUA/IACS), C. Miskey (GSFC/CUA/IACS), A. de Koter (Amsterdam), M. Smith Neubig (CUA/IACS), N Walborn (STScI), T. Lanz (GSFC/AURA)
We have obtained slitless two-dimensional ultraviolet spectroscopy using the Space Telescope Imaging Spectrograph (STIS) aboard the HST of the brightest concentration of OB stars in the faint irregular galaxy, Sextans A. The spectral image obtained with the G140L grating samples a 25'x25" region spanning a wavelength range approximately from 1170 to 1730 A. Sextans A lies at the edge of the Local Group at a distance of 1.4 Mpc and has an extremely low metallicity, roughly 1/30 solar or about 1/3 that of the Small Magellanic Cloud. This is within a factor of two of the most metal deficient galaxy known, I Zw 18. The STIS dataset is unique in that it represents spectra of individual O and B stars at the lowest metallicity ever obtained. The earliest and one of the UV-brightest stars we classify as O6 V based upon comparisons with UV spectra of SMC stars. This star exhibits a definite N V 1240 P Cygni profile that appears only slightly weaker, but with a lower terminal velocity than its SMC analogues. Both C IV and Si IV are also very weak. Absorption from Fe V is also detectable near 1430 and 1450 Angstroms. Other very UV-luminous stars are also present. Several early B-supergiants are also detected as evidenced by the pronounced Si IV 1400 A absorption. Further detailed modeling of the UV spectra using sophisticated model atmosphere codes is planned.