1999A&A...348.1020A

We have observed both Comets Hyakutake and Hale-Bopp close to perigee with several telescopes at frequencies between 30 and 860GHz for an extended period of time. The observed ``light" curves can be described as a simple function of heliocentric and geocentric distances without any outburst or noticeable variability with time. Our most sensitive diameter estimate for C/Hyakutake resulted in an upper limit of 2.1km. The nuclear diameter of C/Hale-Bopp was determined to 44.2km after separation from the halo emission. The central part of both halos can be represented by a Gaussian with a linear size at half power points of 1870 and 11080km for Hyakutake and Hale-Bopp, respectively. The spectral index for both comets is α=2.8, indicating a similar particle size distributions in the halo of these comets. For Hale-Bopp the extended emission could be traced to more than 10⁵km from its nucleus. The derived masses, contained in the halo depend strongly on the assumed physical properties of the halo particles. With κ(1mm)=75cm²/g, possibly more appropriate for comets, a halo mass of 6 10¹⁰ g is derived for Hyakutake and of 8x10¹²g for Hale-Bopp.