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Astron. Astrophys. 349, 649-659 (1999)

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5. Summary

The nuclear radii estimates derived here for an assumed albedo of 0.04 range from 0.9 [FORMULA] rN [FORMULA] 7.1 km, which is typical for previously observed short period comets. After comparison of these estimates with previous observations it was possible to derive lower limits to the fraction of active area at the time the previous observations were taken. Unusually high values of [FORMULA] 19.9%, [FORMULA] 29.5% and [FORMULA] 41.3% were found for 9P/Tempel 1, 81P/Wild 2 and 87P/Bus respectively. The other lower limits derived ranged from 0.3-8.5%. Roughly 50% of the comets observed displayed activity, with [FORMULA] values ranging from 5.9-228.8 cm. In certain cases such as 74P/Smirnova-Chernykh the observed activity was substantial and probably continuous throughout its entire orbit. Comparison of previous [FORMULA] values with those derived here for 87P/Bus reveal that the production of dust as a function of position in its orbit is not the same from one orbit to the next. No correlation of dust colour with heliocentric distance was found, which is consistent with previous studies.

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© European Southern Observatory (ESO) 1999

Online publication: September 2, 1999