Results from Narrowband Photometry of Comet Hale-Bopp (1995 O1)

D. G. Schleicher, R. L. Millis, T. L. Farnham (Lowell Obs.), S. M. Lederer (U. Florida)

We present the results from analysis of narrowband photometry of Comet Hale-Bopp (1995 O1) obtained at Lowell Observatory on 57 nights from July 1995 to May 1997. The IHW comet filters were used to isolate emission from and measure production rates for OH, NH, CN, C tex2html_wrap_inline23 , C tex2html_wrap_inline25 , and to isolate the continuum and derive a proxy for dust production, tex2html_wrap_inline27 . Over this interval, Comet Hale-Bopp typically produced gas and dust at rates of 20 and 100 times greater, respectively, than we observed at the same heliocentric distances for Comet Halley in 1985/86. Even at 7 AU, Hale-Bopp was producing dust at a rate greater than we have measured for any other comet at any distance during 21 years of photometry of more than 100 comets. Photometry of Hale-Bopp obtained near perihelion yield peak production rates (Q(X) molecules/sec) of: 430 for OH, 1.528 for CN, and 1.628 for C tex2html_wrap_inline23 . Peak dust production ( tex2html_wrap_inline27 ) was 1.26 cm. The ratio of the trace species to water (as measured by OH) classifies this comet as ``typical'' in our current compositional taxonomy [cf. A'Hearn et al., 1995, 118 223-270], similar to that of other long-period comets.

From the observed production rate of OH, we calculate the minimum diameter of Hale-Bopp's nucleus to be 17 km. However, the observed presence of persistent jets in the coma suggests that most activity emanates from localized sources, implying that the actual diameter of the nucleus is substantially larger. These results, together with details of Hale-Bopp's production rate variations with heliocentric distance, will be presented. This research was supported by NASA.