The Long Wavelength EUVE Spectrum of the Hot DA White Dwarf G191-B2B

Details The Long Wavelength EUVE Spectrum of the Hot DA White Dwarf G191-B2B The Long Wavelength EUVE Spectrum of the Hot DA White Dwarf G191-B2B

May 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...182.4103d&link_type=abstract

American Astronomical Society, 182nd AAS Meeting, #41.03; Bulletin of the American Astronomical Society, Vol. 25, p.860

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Scientific paper

We report observations by the Extreme Ultraviolet Explorer (EUVE) of the spectrum of the hot DA white dwarf G191-B2B. G191-B2B was detected in the medium and long wavelength channels of the spectrometer and exhibits a rich complex of absorption lines, indicating the presence of traces of heavy elements in its otherwise hydrogen-rich photosphere. We have accounted for a number of instrumental effects, including fixed pattern noise and the presence of overlapping spectral orders. The absorption edge of interstellar HeI at 504 Angstroms is clearly detected in the long wavelength (LW) spectrum. We report here a preliminary analysis of the LW spectrum of G191-B2B with a grid of synthetic spectra incorporating new opacities of iron computed by the Opacity Project. As a first step in the analysis of the G191-B2B spectrum, we have determined the interstellar columns of neutral hydrogen and neutral helium in the line of sight of this star. The measured column for HI is 2.0+/-0.2times 10(18) cm(-2) and the measured HeI/HI is 0.07+/-0.01 for effective temperatures of 55000-60000 K and log g = 7.5. This preliminary analysis indicates a slightly higher value for the ISM column than that reported by HUT. Our results implies a neutral hydrogen to neutral helium ratio of ~ 14, favoring higher ionization of helium in the local interstellar medium if we assume a cosmic abundance ratio of 10 for this ratio. This work has been supported by NASA's EUVE Guest Observer Program.

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