Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.2001b&link_type=abstract
American Astronomical Society, DPS meeting #41, #20.01
Astronomy and Astrophysics
Astronomy
Scientific paper
Measuring the thermal emission of cometary nuclei allows the determination of albedo-independent sizes for comets that are not visited by space probes. In the IR, the atmosphere makes such observations difficult from the ground, so that space telescopes (ISO, Spitzer) are frequently used to observe cometary nuclei. In the millimeter range, single dish observations are mainly sensitive to the dust coma. Interferometric measurements are required but restricted up to now to two cometary nuclei from the Oort cloud (Hyakutake, Hale-Bopp).
The Halley type comet 8P/Tuttle made a close approach to the Earth in January 2008 (geocentric distance of 0.25 AU). Previous studies suggested that its nucleus was large (7.8 km radius) and faintly active. As a result this comet was a good target for interferometric observations of its nucleus thermal emission at millimeter wavelengths.
8P/Tuttle was observed at 240 GHz (1.25 mm) with the IRAM interferometer on the Plateau de Bure in January 2008. The thermal emission of the nucleus was detected and found to be lower than expected, corresponding to an apparent radius close to 2 km. Independant observations carried out with Hubble and Spitzer space telescopes indicate a slightly larger size (2.8 km radius) and were used to build a shape and thermal emission model of 8P nucleus (Groussin et al., A&A suubmitted). We used this model to interpret the Plateau de Bure data and we present here the results of this analysis.
Observations of cometary nuclei in millimeter interferometry will grow up in number in the forthcoming years with the upgrading of current instruments and the opening of ALMA. This will increase the sample of observed nuclei from all the comet dynamic classes and enable further studies of their physical properties.
Biver Nicolas
Bockelée-Morvan Dominique
Boissier Jérémie
Colom Pierre
Crovisier Jacques
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