Dust disks around hot white dwarfs and central stars of planetary nebulae

circumstellar matter;infrared;planetary nebulae;white dwarfs

Bilikova, Jana

关键词: circumstellar matter;    infrared;    planetary nebulae;    white dwarfs;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/32009/Bilikova_Jana.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Two types of dust disks have been discovered around white dwarfs(WDs): small dust disks within the Roche limits of their WDs, and alarge dust disk around the hot central WD of the Helix planetary nebula(PN), possibly produced by collisions among Kuiper Belt-likeobjects.To search for more dust disks of the latter type, we havecarried out a Spitzer MIPS 24 um survey of 71 hot WDs orpre-WDs, and found nine WDs with excess 24 um emission, seven ofwhich are still central stars of planetary nebulae (CSPNs). We havetherefore used archival Spitzer IRAC and MIPS observations ofPNe to search for CSPNs with excess IR emission, and found fiveadditional IR excesses likely originating from dust disks.For some of these CSPNs, we have acquired follow-up Spitzer MIPSimages and IRS spectra, and Gemini NIRI and Michelle spectroscopicobservations. The spectral energy distributions show great diversity inthe emission characteristics of the IR excesses, which may implydifferent mechanisms responsible for the excess emission. The two mostlikely dust production mechanisms are: (1) breakup of bodies inplanetesimal belts through collisions, (2) formation of circumstellardust disks through binary interactions.In addition, we have derived basic dust disk parameters using simpleblackbody approximations, or optically thin dust disk models withrealistic grain and disk properties. The dust disk physical parametersfor CSPNs without near-IR excesses appear consistent with the originas collisionally disrupted planetesimals. The dust disks around CSPNswith near-IR excesses are likely optically thick, and possiblydescended from binary post-AGB stars.The Helix Nebula's CSPN is also associated with a hard X-ray pointsource, whose origin is not known. We have correlated theGalactic WDcatalog with the XMM-Newton and ROSATpoint 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 withhard X-ray emission are known to have excess IR emission.A better understanding of post-AGB binary evolution as well as debrisdisk evolution along with its parent star is needed to distinguishbetween these different origins.Future observations to betterestablish the physical parameters of the dust disks and the presenceof companions are needed for models to discern between the possibledust production mechanisms.