Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1980
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1980a%26a....86..139w&link_type=abstract
Astronomy and Astrophysics, vol. 86, no. 1-2, June 1980, p. 139-148.
Astronomy and Astrophysics
Astrophysics
30
Line Spectra, Metallic Stars, Spectrum Analysis, Stellar Atmospheres, Stellar Spectrophotometry, White Dwarf Stars, Abundance, Atmospheric Models, Calcium, Chemical Composition, Digital Data, Helium, High Resolution, Stellar Envelopes, Stellar Mass Accretion, Stellar Temperature, Van Der Waals Forces
Scientific paper
Extensive new digital spectrophotometry and Greenstein's (1976) multichannel colors are compared with synthetic spectra from blanketed model atmospheres in order to derive atmospheric parameters for the strongly-blanketed white dwarf G 165-7. The star is metal deficient despite enormous optical blanketing, and the relative abundances for heavy elements are not inconsistent with solar ratios, except for calcium which may be depleted an additional factor of three. Possible explanations for the existence of some metals in the atmospheres of a few helium-atmosphere white dwarfs are discussed, including envelope convection during the cooling process, a circulation process, and accretion from the interstellar medium. The spectrum of G 165-7 shows a strong asymmetry in the Mg I 5175 A 'b' profile, and it is suggested that the extended blue wing is caused by a static (rather than impact) van der Waals interaction with neutral helium perturbers; this may be the first identification of such a profile in an astrophysical object.
Liebert James
Wehrse Rainer
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