The circumstellar nature of the metallic features in a hot DA white dwarf

Details The circumstellar nature of the metallic features in a hot DA white dwarf The circumstellar nature of the metallic features in a hot DA white dwarf

Apr 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...443..753h&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 443, no. 2, p. 753-763

Astronomy and Astrophysics

Astronomy

22

Absorption Spectra, Abundance, Carbon, Metallicity, Radial Velocity, Silicon, Stellar Envelopes, Ultraviolet Astronomy, White Dwarf Stars, Atomic Collisions, Density (Mass/Volume), Electron Density (Concentration), Energy Levels, Iue, Photoexcitation, Photosphere, Velocity

Scientific paper

A new co-added IUE echelle spectrum of the bright DA white dwarf CD -38 deg 10980, together with a newly determined radial velocity for this star, indicate that the sharp lined Si and C absorption features seen in the UV are clearly circumstellar in origin. Absorption in both excited and ground state transitions occurs at a velocity displaced by -12.1 +/- 2.0 km.s with respect to the photospheric velocity. Weak features due to the Si IV doublet are seen at a velocity intermediate between that of the circumstellar features and the photosphere. First time estimates of column densities for excited and ground states of C II, Si II, and Si III are derived. These quantities are used with electron density estimates derived from these species to determine the location and physical conditions of the circumstellar gas in the vicinity of CD -38 deg 10980. If collisional excitation alone is responsible for the excited levels of Si III observed in CD -38 deg 10980, then electron densities in the circumstellar gas must exceed 109/cu cm. Substantially lower electron densities are possible if the circumstellar gas is located near enough to the star so that photoexcitation is the dominant process responsible for the excited lines seen in the UV. Strong limits are placed on the photospheric abundance of Si and C in the star itself. These limits are in sharp contrast to the theoretical predictions of radiative levitation in which Si, but not C, is expected in the photosphere of a white dwarf such as CD -38 deg 10980. The interstellar line of sight to CD -38 deg 10980 is also investigated.

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