Discovery of CA II absorption at 1840 angstrom in IUE spectra of two helium-rich white dwarfs.

The spectrum of the white dwarf star L 745-46 A, which is classified as DF because of the presence of Ca II H and K lines in the visible region, is found to contain the strong Ca II 1840 A absorption line in the IUE short wavelength region. The same line is more weakly in evidence in the short wavelength IUE spectrum of L 791-40, which is a DC star recently reclassified DB in view of the presence of weak He lines and otherwise exhibiting a strong C I line spectrum that is similar to that of the DC star L 79-3. The C and Ca abundances of L 791-40 establish it to be an intermediate case between the He-rich white dwarf spectral types DB, DC, C2 and DF.