Calcium in the helium white dwarf GD 40

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.