Monitoring the CO Emission of 29P/SW1 in December 1996

M.C. Festou (Midi Pyrénées Obs.), M. Gunnarson, H. Rickman (Uppsala Obs.), G. Tancredi (Montevideo University), A. Winnberg (Onsala Obs.)

Comet 29P/SW1 was monitored at 230 GHz (BWHM of 22) with the Swedish European Southern Observatory 15 m antenna during the whole month of December 1996. CO emission is detected in all averaged daily runs, providing thus a unique set of observations in which the line position, width and flux can be measured. The comet was active at all times and its visual magnitude was of order 16. The CO production irregularly oscillated between extreme rates that did not differ in 32 days by more than a factor of tex2html_wrap_inline11 . A strong sunward emission is always present at tex2html_wrap_inline13 km/s and shows a strong peak whose width is very narrow ( tex2html_wrap_inline15 km/s), which is indicative of a very low rotational temperature. The line position and structure remained remarkably stable. Data accumulated over a period of tex2html_wrap_inline17 sec show the "ON" spectrum with a very high S/N that allows us to model the 3D structure of the CO cloud. Besides the main peak exists a skirt that becomes a double peak structure in offset spectra taken at, respectively, 11 and 22on the sunward side. These observations allow to fully describe the outgassing and activity patterns of the nucleus of comet P/SW1 over a one-month period..