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H.L. Shipman (University of Delaware), J.L. Provencal (Mt. Cuba Observatory, University of Delaware), H.L. Shipman, J. MacDonald (University of Delaware)
We present UV STIS observations of the massive DQ white dwarfs G227-5 and G35-26. One of the largest uncertainties in theoretical ages of white dwarf stars is their unknown core composition. DQ white dwarfs are helium-rich stars displaying carbon in their spectra. The observed carbon is believed to result from dredge-up of the underlying core by the helium convection zone. Theoretical work argues that oxygen should also be present in detectable amounts in more massive white dwarfs. Our initial goal is the determination of the ratio of carbon and oxygen in these white dwarfs.
Our spectra cover 1295 to 1350 Å. We find lines of N I, O I, Si II, and C II in emission. Preliminary abundance analysis argue that the features arise in oxygen-rich chromospheres. These white dwarfs, with temperatures around 13,000 K, are the hottest stars with detected chromospheres.
This work is based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operatied by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. This work is also funded by grant HST-GO-08649.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.