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D. G. Schleicher, R. L. Millis (Lowell Obs.)
We present results from narrowband photometry of Comet 67P/Churyumov-Gerasimenko, the new target of ESA's ROSETTA mission. A total of 16 nights of observations were obtained at Lowell Observatory during the 1982/3 and 1995/6 apparitions. These data encompass an interval of -61 to +118 days from perihelion, corresponding to a range of heliocentric distances before perihelion from 1.48 to 1.34 AU, and an outbound range from 1.30 to 1.86 AU. Production rates were determined for OH, NH, CN, C3, and C2, along with A(\theta)f\rho, a measure of the dust production. Water production, based on OH, has a steep (~ -5) r-dependence post-perihelion, while minor species and dust are less steep (~ -2 to -3). All species exhibit larger production rates following perihelion, with water having a ~2\times pre/post-perihelion asymmetry, while minor species and dust have a larger asymmetry. The asymmetry implies a strong seasonal effect and probable high obliquity of the rotational axis, along with one or more isolated source regions coming into sunlight near perihelion. Peak water production (which occured about 1 month after perihelion) was ~1.0\times1028 mol s-1 and, when combined with a standard water vaporization model, implies an effective active area on the surface of the nucleus of ~2~km2. Abundances of carbon-chain molecules yield a classification of slightly ``depleted'' in the A'Hearn et al. (1995, Icarus 118, 223-270) database. The peak dust production (as measured by A(\theta)f\rho) was ~450 cm, while the color of the dust is slightly reddened. In comparison to original ROSETTA target Comet 46P/Wirtanen, Comet Churyumov-Gerasimenko has essentially the same peak water production and a peak dust production about 3\times greater than does Wirtanen (assuming that the properties of the dust grains are similar) (cf. Farnham and Schleicher (1998, A&A 335, L50-55).
This research was supported by NASA.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.