Calcium in the helium white dwarf GD 40

Details Calcium in the helium white dwarf GD 40 Calcium in the helium white dwarf GD 40

Jul 1977

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977aj.....82..480s&link_type=abstract

Astronomical Journal, vol. 82, July 1977, p. 480-486. Research supported by the Research Corp., University of Delaware, and NSF.

Astronomy and Astrophysics

Astronomy

21

Abundance, Calcium, Line Spectra, Stellar Atmospheres, Stellar Spectra, White Dwarf Stars, H Lines, Helium, K Lines, Stellar Gravitation, Stellar Models, Stellar Rotation, Stellar Temperature

Scientific paper

The paper examines spectra of the DB white dwarf GD 40, the only DB star known which shows Ca II lines in its spectrum. Ten helium lines are visible along with the H and K lines of Ca II. An analysis of the spectrum gives an effective temperature of approximately 15,200 K, log g of about 8.2, and a logarithmic calcium abundance (relative to helium) of approximately -7.5, assuming that helium is the only donor of electrons in the atmosphere. The results are only slightly different if metallic electron donors are present, even in solar concentrations. This calcium abundance is higher than in cool metallic-line white dwarfs. The surface gravity was determined from the ratios of weak to strong lines in the He I spectrum.

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