The authors acknowledge the support of the NASA Planetary Astronomy Program and of the NSF Planetary Astronomy Program.

This work has been graciously supported by grants from the NASA Planetary Astronomy and Astrophysical Data Programs.

>From the 60 and 175microns , radial intensity profiles have been derived which are compared to the ones obtained from the near-IR data and to the results of multi-aperture photometry. Since dust grains have the highest thermal emitting efficiency closest to their own size, the emission in the maps observed with the two filters are dominated by the the thermal emission of different size grains. From the comparison of the different wavelength maps, indications on perferred concentration of different grain sizes can be derived. Grain size distribution modeling has been carried out for the spectral energy distribution derived with multi-filter photometry to get an indication of the coma composition with will in turn be used as input for dynamical modeling. First results will be presented.

The morphology of the comet was observed to change from the static 6 to 8 jet "hedgehog" structure in 1996 to the rotating "pinwheel" structure seen in 1997. Light curves taken at perihelion indicate a rotational periodicity of 11.3 hours. The comet was found to be extremely dusty, with a dust/gas the Dust ratio of 8 and an extremely strong silicate emission feature

We present dust production rates, particle size distribu- tions and compositions found by fitting fluffy Mie dust models to the multi-wavelength photometry. We also present estimates for the dust outflow rate and constraints on the rotation state of the nucleus from imaging of the comet over time.

Our program for both comets concentrated on millimeter-wave observations of sulfur bearing molecules in an effort to understand the total sulfur budget of the comet. Using the National Radio Astronomy Observatory 12-m telescope on Kitt Peak we observed H_2S, CS, and OCS. Additionally, in C/Hale-Bopp we monitored the long and short-term variations in these species, and observed H_2CS and SO as well. This was the first observation of H_2CS in any comet.

C/Hale-Bopp is the first comet in which so many sulfur species have been observed. Analysis of the abundances of these species in comparison to the total atomic sulfur observed in both comets should reveal whether or not we can now account for all of the primary sulfur sources in comets. Perhaps the most interesting question that these observations leave unanswered is why C/Hale-Bopp appears to contain so much more SO and SO_2 (as observed by others) than any other comet.

The morphology of the comet was observed to change from the 6 to 8 jet "hedgehog" structure in 1996 to the "pinwheel" structure seen in 1997. Light curves taken at perihelion indicate a rotational periodicity of 11.3 hours. We present dust production rates, dust to gas ratios, and estimates for the particle size distribution and composition found by fitting fluffy Mie dust models to the multi-wavelength photometry.

In the fall of 1996 we observed the periodic comet P/IRAS across a broad range of wavelengths from visible through far-infrared. Narrowband visible imaging and photometry from Lowell Observatory along with near and thermal-infrared imaging and photometry from the NASA/IRTF were coordinated with two mid- and far-IR observing runs using the Infrared Space Observatory. Dynamical and spectral modeling of the resulting data is being used to determine or constrain the composition, particle size distribution, and emission history of the dust emitted by this comet. We present preliminary results from our modeling and establish a framework in which to compare data from other coordinated observing campaigns for comets P/Kopff, C/Hale-Bopp, and P/Wolf-Harrington. Furthermore, we will present a comparison of these results to IRAS and COBE observations of cometary dust.

Our optical data -- images in the IHW narrow-band filters -- have yielded a rotation rate of 0.236 days, but no explicit nuclear signature. Our single VLA track (at a wavelength of 3.55 cm) allowed us to obtain flux density upper-limits that are smaller than any other VLA continuum observation of a comet, and an upper-limit to the radius of about 3 km. By modeling the intensity distribution of the coma, we have extracted the nuclear flux from our thermal-infrared (5 - 21 mu m) images, and obtained an effective nuclear radius of 2.4 +/- 0.5 km. In addition, we present preliminary results from our attempts to simulate the infrared emission from the nucleus using a model that accounts for nuclear ellipticity, rotation, surface heterogeneity, and material properties.

The nucleus and near-nuclear region of the comet is a poorly studied region, owing to the typically-large geocentric distances ( ~ 1 AU) which cause the flux from the coma to overwhelm any information we would get from the nucleus. In addition, gas and dust emission and small effective radii contribute to the difficulties. Thus, nuclear properties are well-known for only a handful of specimens.

The IRTF (19 - 22 and 24 - 25 Mar) and KPNO (19 - 23 Mar) observations were performed almost all simultaneously. The temporal coincidence of these data was a key aspect in determining properties of the nucleus; data from the two sets of wavelengths allowed us to differentiate between scattered sunlight and intrinsic emission. Observations at IRTF employed two cameras, NSFCAM (1-5 mu m) and MIRAC2 (10 mu m). Our VLA observations were performed on 27 March, observing the comet at 3.6 cm in an attempt to detect the comet's thermal microwave continuum emission. We present here results from the preliminary reduction of data from all three wavelength regimes.