Resolving the Dust Disk Around the Central Star of the Helix Nebula

Details Resolving the Dust Disk Around the Central Star of the Helix Nebula Resolving the Dust Disk Around the Central Star of the Helix Nebula

Feb 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007noao.prop..411s&link_type=abstract

NOAO Proposal ID #2007A-0411

Computer Science

Scientific paper

The central star of the Helix Nebula is a hot white dwarf with a stellar effective temperature of 120,000 K. Recent Spitzer observations of the Helix Nebula revealed an infrared excess emission associated with the central star, detected from ~8 to ~70 (mu)m. This excess emission appears to be point-like at all Spitzer bands. In the 24 (micron) band, a region of diffuse emission surrounds the central source, and a Spitzer IRS spectrum shows that this diffuse emission is dominated by nebular [O IV] 25.89 (micron) line. It is very unlikely that the central source originates from emission lines because the compact source is not detected in He II line image and the Spitzer MIPS 70 (micron) band does not contain strong high-ionization nebular lines. The spectral energy distribution of the central source is consistent with a dust continuum for temperatures of 100-130 K, which requires a radial distance of 82-139 AU and an emitting area of 3.4-6.7 AU^2, if the emission is blackbody-like. Such temperature and emitting area can be explained only by a debris disk around this hot WD, analogous to those reported around white dwarfs GD 362 and G 29-38. The survival of debris disk through stellar evolution with the ejection of a planetary nebula is most intriguing. We have a scheduled Spitzer IRS follow-up observation to further constrain the dust compositions in the disk. Here we propose to image the Helix central star with Gemini-North + Michelle at 18.5 (micron) to place stringent constraints on the size of the disk.

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