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A test of the planet–star unipolar inductor for magnetic white dwarfs

“…Historically, DQ stars were modelled with helium atmospheres (e.g. Bues 1973;Grenfell 1974;Wegner & Yackovich 1984), but there is now a significant body of evidence that the warmer and hot DQ stars have little or no helium, and are instead bare stellar cores that just avoided detonation as supernovae, and thus have significant carbon and oxygen in their atmospheres (Dufour et al 2007(Dufour et al , 2008. In this picture, the observed emission lines from G227-5 and G35-26 are intrinsic and reflect the composition of the atmosphere, and thus the composition of the outer layers of a stellar core.…”

Detailed Spectroscopic and Photometric Analysis of DQ White Dwarfs

“…Cool white dwarfs showing traces of carbon, either as neutral carbon lines or molecular C 2 Swan bands, are collectively known as DQ stars. Past analyses showed that these stars are helium rich with carbon abundances ranging from log C/He = −7 to −2 as determined from optical or ultraviolet (IUE) spectroscopic observations (Bues 1973;Grenfell 1974;Koester et al 1982;Wegner & Yackovich 1984;Weidemann & Koester 1995).…”

“…Past analyses have shown that these stars have helium-rich atmospheres with carbon abundances ranging from log (C/He) ¼ À7 to À2, as determined from optical or ultraviolet (mainly International Ultraviolet Explorer [IUE ]) spectroscopic observations (Bues 1973;Grenfell 1974;Koester et al 1982;Wegner & Yackovich 1984;Weidemann & Koester 1995). The presence of carbon in the atmosphere of these objects has been successfully explained by a model in which carbon diffusing upward from the core is brought to the photosphere by the deep helium convection zone (Pelletier et al 1986).…”