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N. F. Baugh (Augusta St. U.), D. G. Schleicher (Lowell Obs.)
During a four-year interval, more than 90 nights of narrowband photometry were obtained of Comet Hale--Bopp (1995 O1) from the Lowell and Perth Observatories. Because these observations cover an extremely large range of heliocentric distances (r), the variation of gas production rates with r can be used to probe each species' release from the nucleus as a function of solar illumination and temperature. Unfortunately, Hale-Bopp's very high total gas production when it was closer than about 2-3 AU from the Sun resulted in unusually high gas outflow velocities as compared to other comets. Therefore, canonical scalelengths do not adequately reproduce the spatial distribution of the observed gas species, OH, NH, CN, C2, and C3, at small r. Based on narrowband images obtained at perihelion, Schleicher et al. (1999, BAAS 31, 1128) determined that most species' parent and daughter Haser scalelengths needed to be increased by 2-3\times the canonical values to reproduce the bulk radial fall-off for each gas species, yielding perihelion production rates 1.1-3.6\times larger than otherwise calculated, with water exhibiting the largest correction.
So that the entire Lowell/Perth dataset can be reduced to absolute production rates, we have now begun an effort to determine appropriate scalelengths for Hale-Bopp between about 3.5 AU and perihelion, which can be combined with the recently reported results from modeling spatial profiles beyond 2.8 AU by Rauer et al. (2003, A&A 397, 1109-1122). We anticipate reporting on preliminary findings of this investigation, including scalelengths and r-dependencies which can be used to accurately extrapolate aperture photometry measurements to total coma abundances, as well as resulting absolute gas production rates.
This research is supported by NASA and the NSF REU program.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.