The First Medium-Resolution Far-Ultraviolet Photometric Atlas of Hot Star Spectra

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Session 20 -- Astro 2
Display presentation, Tuesday, June 13, 1995, 9:20am - 6:30pm

[20.09] The First Medium-Resolution Far-Ultraviolet Photometric Atlas of Hot Star Spectra

R.H.Buss Jr., J.W.Kruk (JHU), H.C.Ferguson (STScI)

The intrinsic spectral energy distributions of hot stars are strongest in the far-ultraviolet (FUV; 912--1824~\AA). The distributions are important because they both determine the radiation field of star-forming galaxies and because they exhibit the stellar atmospheric properties of luminous stars. We present a photometric, FUV spectral atlas of the intrinsic energy distributions of OB stars, as corrected for extinction by the Galactic medium. The 3~\AA\ resolution FUV spectra, mostly of lightly-reddened dwarf and giant stars, were observed by the Hopkins Ultraviolet Telescope on the ASTRO-2 shuttle mission in March 1995. The spectra show many stellar atmospheric absorption lines from cosmically-abundant elements, such as C, N, H, He, and Fe, on the stellar emission continuum down to the 912~\AA\ HI Lyman limit. We calibrate the OB star fluxes with comparison spectral observations of standard white-dwarfs; the adopted OB star extinction parameters range from $R_V=3.0$--3.7; and in most cases, correction for ISM H$_2$ absorption from 912--1110~\AA\ is negligible or small. For stars hotter than B2.5V ($T=20,000$~K), we corrected HI Ly-$\alpha$ absorption wings from the Galactic Medium. Thus, the calibrated spectra represent the intrinsic FUV stellar emission from hot stars , and as such, can be used for atmospheric modeling, population synthesis, radiation fields in ISM clouds, dust extinction, and hopefully other purposes. We illustrate applications of the atlas by 1) deriving the extinction by Galactic dust along other sight-lines toward reddened stars and 2) comparing the spectra with model atmospheres in the FUV.

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