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Title:Dust disks around hot white dwarfs and central stars of planetary nebulae
Author(s):Bilikova, Jana
Director of Research:Chu, You-Hua
Doctoral Committee Chair(s):Chu, You-Hua
Doctoral Committee Member(s):Gammie, Charles F.; Su, Kate Y.; Thompson, Laird A.; Looney, Leslie W.; Webbink, Ronald F.
Department / Program:Astronomy
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):circumstellar matter
planetary nebulae
white dwarfs
Abstract:Two types of dust disks have been discovered around white dwarfs (WDs): small dust disks within the Roche limits of their WDs, and a large dust disk around the hot central WD of the Helix planetary nebula (PN), possibly produced by collisions among Kuiper Belt-like objects.To search for more dust disks of the latter type, we have carried out a Spitzer MIPS 24 um survey of 71 hot WDs or pre-WDs, and found nine WDs with excess 24 um emission, seven of which are still central stars of planetary nebulae (CSPNs). We have therefore used archival Spitzer IRAC and MIPS observations of PNe to search for CSPNs with excess IR emission, and found five additional IR excesses likely originating from dust disks. For some of these CSPNs, we have acquired follow-up Spitzer MIPS images and IRS spectra, and Gemini NIRI and Michelle spectroscopic observations. The spectral energy distributions show great diversity in the emission characteristics of the IR excesses, which may imply different mechanisms responsible for the excess emission. The two most likely dust production mechanisms are: (1) breakup of bodies in planetesimal belts through collisions, (2) formation of circumstellar dust disks through binary interactions. In addition, we have derived basic dust disk parameters using simple blackbody approximations, or optically thin dust disk models with realistic grain and disk properties. The dust disk physical parameters for CSPNs without near-IR excesses appear consistent with the origin as collisionally disrupted planetesimals. The dust disks around CSPNs with near-IR excesses are likely optically thick, and possibly descended from binary post-AGB stars. The Helix Nebula's CSPN is also associated with a hard X-ray point source, whose origin is not known. We have correlated the Galactic WD catalog with the XMM-Newton and ROSAT point source catalogs to search for more single WDs with hard X-ray emission. Apart from the central WD of the Helix Nebula, none of the single WDs with hard X-ray emission are known to have excess IR emission. A better understanding of post-AGB binary evolution as well as debris disk evolution along with its parent star is needed to distinguish between these different origins.Future observations to better establish the physical parameters of the dust disks and the presence of companions are needed for models to discern between the possible dust production mechanisms.
Issue Date:2012-06-27
Rights Information:American Astronomical Society (2010, 2011,2012)
Date Available in IDEALS:2014-06-28
Date Deposited:2012-05

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