AAS 200th meeting, Albuquerque, NM, June 2002
Session 72. Degenerates
Display, Thursday, June 6, 2002, 9:20am-4:00pm, SW Exhibit Hall

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[72.06] Extension of the DBV White Dwarf Instability Strip: PG0112+104 Pulsates

H.L. Shipman (U. Delaware), J. Provencal (Mt. Cuba Astronomical Obs., and U. Delaware), R. Riddle, M. Vuckovic (Iowa State U. )

PG0112+104 is the only known DB white dwarf between 28,000 K and 30,000 K. This single object defines the DB gap's observed red edge and the empirical blue edge of the helium instability strip. Provencal et al. find a hydrogen abundance of log(H/He) ~ -3.8, the highest surface abundance of the three DBs studied, as expected if this star has just remixed its thin DA mantle and emerged from the DB gap (Provencal, J. L.; Shipman, H. L.; Thejll, P.; Vennes, Stéphane. 2000. Ap.J. 542, 1041-1056.) Based on the width of the C II lines, Provencal et al. suggested that there might be substantial horizontal surface motions.

We obtained 30 hours of white-light, high-speed photometry from 5 runs spanning five days during 2001 October with the McDonald Observatory 2.1m telescope, the Whole Earth Telescope (WET) standard three channel photometer, and the standard data reduction program of Nather et al. (1990). The data shows that the star is indeed variable on time scales similar to the time scales of other DBV variables, pulsating in nonradial g-modes with periods ranging from 100 to 1000 s. The amplitude and power spectrum of the variability is consistent with previously published upper limits on this star. We present a light curve and a power spectrum. As bells constructed using a range of shapes and materials ring with different tones, white dwarfs with differing structure and composition pulsate with different frequencies. Data like ours may permit us to determine the envelope structure of this star and compare it to the structure of other DBV variables.

Our research on the space ultraviolet properties of DBV stars has been supported by the Space Telescope Science Institute; the Annie Jump Cannon Fund supported our observing trip.

The author(s) of this abstract have provided an email address for comments about the abstract: harrys@udel.edu

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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.