Multiwavelength Observations of the Nucleus and Coma of Comet Hale-Bopp

Y. R. Fernández, C. M. Lisse, D. D. Wellnitz, M. F. A'Hearn, A. Kundu (U.Md.), M. W. Buie, E. W. Dunham, R. L. Millis, R. A. Nye, J. A. Stansberry, L. H. Wasserman (Lowell Obs.), M. E. Golden, M. Persson (MIT), R. R. Howell (U.Wy.), R. L. Marcialis, J. N. Spitale (LPL), W. F. Hoffmann, A. Dayal (U.Az.), L. K. Deutsch (Bos.U.), G. G. Fazio (CfA), J. L. Hora (IfA), M. S. Hanner, M. Ressler (JPL), T. Kostiuk, T. A. Livengood (NASA/GSFC)

We present multiwavelength observations of the nucleus and coma of the bright, giant comet C/1995 O1 (Hale-Bopp) in the optical, IR, and radio regimes. The nucleus was observed by NRAO's Very Large Array in a 66-hr observation, during 20 to 27 Mar 1997. This is the first detection of the nuclear thermal continuum radiation from a comet at that observatory. We also observed the occultation by the comet's nucleus and inner coma of a ninth-magnitude star on 5 October 1996; the analysis of the light-curve corroborates our microwave nuclear results, and also shows the inner coma of Hale-Bopp to be optically thick. To our knowledge, only one other comet nucleus was observed to occult a star with such a small impact parameter (the low-activity comet 95P/Chiron). We also present preliminary analyses of thermal-infrared imaging of the comet taken at NASA/IRTF (with the MIRAC2 and MIRLIN cameras) near perihelion. These data show the comet's rotation period, via the comatic morphology. We are working to explain the rotational behavior of the nucleus, as well as model the thermal behavior of Hale-Bopp's nucleus in all wavelength regimes.