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N. Biver, D. Bockelée-Morvan, J. Crovisier, P. Colom, A. Lecacheux, F. Henry (LESIA, Obs. de Paris), G. Paubert (IRAM-Granada, Spain), R. Moreno (IRAM-Grenoble, France)
Comets C/2002~X5 (Kudo-Fujikawa) and C/2002~V1 (NEAT), discovered in fall 2002, have been the brightest comets to come closer than 0.2 AU from the Sun for several years. Target-of-opportunity observations of both comets were made at IRAM close to their perihelion, at 0.19 AU on Jan. 29, 2003, for C/2002~X5 and 0.10 AU on Feb. 18, for C/2002~V1. In addition, C/2002~X5 was observed at 0.55 AU pre-perihelion and 1.18 AU post-perihelion. The water outgassing rate was monitored almost daily from the observations of the OH radical with the Nançay radio-telescope between Jan. 1 and April 9 (C/2002~X5) and Dec. 31, 2002 and April 26 (C/2002~V1). The Odin satellite also observed and detected the water line at 557~GHz in C/2002~X5 between March 3 and 30, 2003.
The near perihelion observations at IRAM were challenging because of small solar elongations (5-8\circ) and lack of precise astrometry at that time.
HCN, CS, CH3OH and HNC were detected in both comets. CH3CN and HC3N were also detected in C/2002~X5. The high S/N (>50) detections of the HCN(3-2) line at 0.21 and 0.11 AU show that the maximum gas velocity observed in both comets did not exceed 2.1 km/s. The HNC/HCN ratio was found to be around 20% at 0.2--0.1 AU, similar to the maximum value observed in other comets. We may have expected a higher ratio if HNC was produced by the thermal degradation of organic grains. The detection of CS very close to the Sun provides constraints on its photodissociation. Upper limits on other species abundances will be presented and the origin of molecular species in the coma will be discussed.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.