DPS 2001 meeting, November 2001
Session 43. Comet C/2001 A2 (LINEAR)
Oral, Chair: M. A'Hearn, Friday, November 30, 2001, 11:30am-12:30pm, Regency E

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[43.06] Spectroscopic Investigation of Comets C/1999 T1 (McNaught-Hartley) and C/2001 A2 (LINEAR) at Radio Wavelengths: Evidence for Chemical Diversity

J. Crovisier (Obs. de Paris), N. Biver (ESA, ESTEC & Obs. de Paris), R. Moreno (IRAM, Grenoble), D.C. Lis (Caltech), D. Bockelée-Morvan (Obs. de Paris), M. Womack (St. Cloud State University), P. Colom, F. Henry, A. Lecacheux (Obs. de Paris), G. Paubert (IRAM, Granada), D. Despois (Obs. de Bordeaux), H.A. Weaver (Johns Hopkins University, Baltimore)

Comet C/1999 T1 (McNaught-Hartley) was observed at radio wavelengths using the Swedish-ESO Submillimetre Telescope (SEST), Caltech Submillimeter Observatory (CSO), Institut de RadioAstronomie Millimétrique (IRAM) 30-m, and Nançay telescopes between September 2000 and February 2001. Comet C/2001 A2 (LINEAR) was also observed with the CSO, IRAM and Nançay telescopes, as well as with the Kitt Peak 12-m Radio Telescope, between April and July 2001. The lines of OH, HCN, CH3OH, H2CO, H2S, CS, were detected in both comets. In addition, CO was detected in C/1999 T1, and HNC and CH3CN were detected in C/2001 A2.

These two Oort cloud comets presented similar intrinsic activity levels, with a water outgassing rate peaking at around 1029 molecules s-1 near perihelion. However, C/2001 A2 showed a much steeper heliocentric evolution of its activity, and a dramatic outburst of \approx 4 magnitudes at 1.3 AU inbound. The gaseous composition of these comets also presents some significant differences: CO is much more abundant (with respect to HCN and CH3OH) in C/1999 T1, while another very volatile molecule, H2S, is more abundant in C/2001 A2. In C/2001 A2, the HNC, CS and H2CO abundances (relative to HCN or H2S and CH3OH) show variations with heliocentric distance and/or cometary activity. Similar behaviors were seen in comet C/1995 O1 (Hale-Bopp). Sensitive searches of HC3N and OCS in C/2001 A2 suggest that these species are depleted with respect to HCN, CH3CN or H2S, in comparison with what was measured in comet Hale-Bopp.

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