AAS 207th Meeting, 8-12 January 2006
Session 205 White Dwarfs
Oral, Thursday, 2:00-3:30pm, January 12, 2006, Salon 1

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[205.03] The Mystery Deepens: Spitzer Observations of Cool White Dwarfs

M. Kilic, T. von Hippel, F. Mullally (University of Texas at Austin), W. T. Reach (Spitzer Science Center), M. J. Kuchner (NASA Goddard Space Flight Center), D. E. Winget (University of Texas at Austin), A. Burrows (University of Arizona)

We present mid-infrared (4.5\mum and 8\mum) photometric observations of 18 cool white dwarfs obtained with the Spitzer Space Telescope. Our observations demonstrate that four DA white dwarfs with T\rm eff< 7000 K show slightly depressed mid-IR fluxes. In addition, two white dwarfs with peculiar optical and near-IR spectral energy distributions (LHS 1126 and G240-72) are found to display significant flux deficits in the Spitzer observations. These mid-IR flux deficits are not predicted by the current white dwarf models including collision induced absorption due to molecular hydrogen. We show that either the collision induced absorption calculations are incomplete or there are other unrecognized physical processes in cool white dwarf atmospheres. The spectral energy distribution of LHS 1126 surprisingly fits a power law (Rayleigh-Jeans spectrum) in the infrared, which implies that the source of this deficit is probably not molecular absorption but some other process.

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Bulletin of the American Astronomical Society, 37 #4
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