Comet Hale-Bopp: A Combined Ground and Space Based Study from 0.5 - 160 

David J. Osip ¹, R. G. Walker ², D. Lien ², S. M. Lederer ³, E. Grün ⁴, & S. Peschke ⁴

¹ Massachusetts Institute of Technology

² Vanguard Research Inc.

³ University of Florida

⁴ MPIK

We report on simultaneous multi-wavelength observations of Comet Hale-Bopp obtained from ground based telescopes and from two spacecraft, the Infrared Space Observatory (ISO) and the Midcourse Space Experiment (MSX). On October 6-10 UT, 1996, we obtained 1-20 micron imaging and spectrophotometry using the BOLO and NSFCAM instruments at the NASA 3.0 meter Infrared Telescope Facility in Hawaii. On October 8-11 UT, 1996, we obtained visible continuum imaging at the Lowell Observatory 1.1 meter Hall telescope, using a TI 800x800 CCD camera and narrowband filters at 4845 and 6840 angstroms. Spectrophotometry spanning 3-160 microns was obtained with the ISOPHOT instrument on October 7 UT, 1996. Finally, thermal images were obtained in 4 wavebands from 6-25 microns using the SPIRIT III telescope aboard MSX also on October 7 UT, 1996. Here, we present a combined analysis of the ground based, ISO, and MSX data and begin to constrain models of the composition and abundance of the coma dust particles.

Initial results include:

• Best fit to the color temperature of grains 270K - significantly above the blackbody temperature of 165K. This implies a size distribution with a significant fraction of grains in the 0.3-0.5 micron range. Modelling of the ISO results by S. Peschke [Earth Moon and Planets in press] also favors small carbonaceous and silicate grains.

• Strong silicate feature at 10 and 20 microns, greater than a factor of 2 above background

• Bolometric Albedo: 0.15 - consistent with that found in Halley and other comets at similar phase angles.

• No color trend in the near infrared data - suggesting that icy-grain sublimation was not an effect after the comet was inside of 3 AU.

• Aperture photometry at visible,near-IR and thermal-IR all consistent with canonical fall-off.

• Ground based photometry confirms mid-IR calibration of both ISOPHOT and MSX SPIRIT III.