Local subgiants and time-scales of disc formation |
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| Authors: | Jan Bernkopf Klaus Fuhrmann † |
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| Institution: | Department of Physics and Astronomy, The University, Sheffield S3 7RH |
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| Abstract: | This paper concentrates on the relationship between the rate of gas emission from the nucleus of Comet 9P/Tempel 1, the fraction f of the nucleus that is active, and the crater damage inflicted by the recent 2005 July 4 Deep Impact space mission. The cometary nucleus has a surface area of about 1.7 × 108 m2 and a mean radius of about 3700 m. Before the impact it is estimated that only a fraction f = 0.0056 of the nucleus surface was actively producing gas and dust. The active area was about 9.4 × 105 m2 . Absolute magnitudes obtained at recent perihelion passages of this comet indicate that variations in the 0.0074 > f > 0.0039 range can occur from apparition to apparition. Because of the low size of the original active area, the production of a new impact crater in the diameter range 40 to 300 m would lead to a long-term change in the cometary visual magnitude in the range 0.0018 to 0.098 respectively. This is below the limit of detectability. It has been suggested that the cometary dust is in the form of 'talcum powder' not 'beach sand'. We suggest that the dust ejected from the impact site has been broken up by the energetic impact process and thus has a different size distribution from dust locked in the snowy matrix of the nucleus and normally lifted off the nucleus by gentle sublimation processes. |
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| Keywords: | comets: general comets: individual: 9P/Tempel 1 |
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