SIMBAD references

The far-ultraviolet (FUV) spectrum of the DA white dwarf PG 1603+432 obtained with the Far Ultraviolet Spectroscopic Explorer reveals the presence of helium and carbon in the atmosphere of the star. Our analysis of the FUV continuum and spectral lines, in particular the He II λ1085 and C III λ1175 line profiles, indicates T_eff=35,075 K, logg=7.96, He/H=0.01, and C/H=1.4x10^–7; we expect high signal-to-noise ratio optical spectroscopy to reveal weak He I λλ4471, 5876 spectral lines. Based on the line-profile analysis, helium appears to be homogeneously distributed in the atmosphere, but the absence of optical helium lines in past observations suggests a lower helium abundance in the optical photosphere relative to the deeper FUV photosphere or a time-variable abundance. PG 1603+432 is only the third DAB white dwarf found to populate the so-called DB gap (30,000-45,000 K), after GD 50 and HS 0209+0832, but this population does not appear to be an extension of the DAO white dwarf sequence toward lower temperatures.