The EUVE and IUE Spectra of the Hot DA White Dwarf GD 659

Details The EUVE and IUE Spectra of the Hot DA White Dwarf GD 659 The EUVE and IUE Spectra of the Hot DA White Dwarf GD 659

Nov 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...453..313h&link_type=abstract

Astrophysical Journal v.453, p.313

Astronomy and Astrophysics

Astronomy

22

Stars: Circumstellar Matter, Stars: Individual Alphanumeric: Gd 659, Ism: Abundances, Ultraviolet: Stars, Stars: White Dwarfs

Scientific paper

We present recent EUVE spectra and new co-added lUE echelle spectra of the hot DA white dwarf GD 659. Our EUVE spectra show the expected continuum of a pure H DA white dwarf, from which we derive upper limits on the photospheric abundances for He, C, N, O, and Si. Our co-added lUE echelle spectrum shows, in addition to the common interstellar lines, weak features due to C IV, N V, and Si IV redshifted 72 km s-1, with respect to the stellar photosphere. No features are seen at the expected stellar velocity. The lack of detectable absorption from strong subordinate lines of lower ionization states of C, N, and Si effectively rules out a photospheric origin for the redshifted features. Instead the redshifted features appear to arise in a highly ionized region either in the immediate circumstellar or interstellar environment of the star. Our derived column densities for these species are compared with predictions for an interaction zone between a weak interstellar wind and an interstellar accretion flow (MacDonald 1992) and with those of a Stromgren sphere (Dupree & Raymond 1983). These models prove inadequate to explain these observed ions. From our EUVE spectra we also obtain interstellar column densities for H I, He I, and He I! along the line of sight to GD 659. From these data we find respective interstellar H and He ionization fractions 0.36±0.17 and 0.36±0.06.

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