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Session 72 - Comet Hale-Bopp.
Display session, Friday, January 09
Exhibit Hall,
The concept of simultaneous multifrequency continuum observations, successfully tested on Comet Hyakutake, was applied to Comet Hale-Bopp, using the Heinrich Hertz Submillimeter Telescope (HHT) with the four color bolometer between 250 and 870 GHz; the IRAM 30m telescope at 250 GHz; the IRAM Plateau de Bure Interferometer near 90 and 240 GHz; and the MPIfR 100m telescope at 32 GHz. Near-simultaneous measurements were done between 1997 February 15 and 1997 April 26, mainly concentrated in mid-March shortly before perigee of the comet.
The measurements gave the following preliminary results: (a) interferometer detection of the nuclear continuum emission. The derived mean diameter is of the order of 50 km. (b) a radio halo with a gaussian HPW of \sim 11 \arcsec, corresponding to a diameter of 11000 km at geocentric distance of 1.2 A.U. (c) a spectral index (SI) of \sim3.0 of the total signal, indicating a particle size distribution in the radio halo between 0.1 and 3 mm.
Assuming an average cometary density of 0.5 g cm^-3, the mass contained in the nucleus is about 3\times 10^19 g and 10^12 g in the particle halo, inferred from the SI.
A more detailed analysis is under way, which includes corrections for the various calibration scales at the different telescopes and the possible contamination of the observed bolometer signal by molecular line emission. We will report on the results of this analysis and the implications for the mm -- submm wavelength radio spectrum of Comet Hale-Bopp.
