OBSERVATIONS OF THE OH RADICAL IN COMET C 1996 B2 (HYAKUTAKE) WITH THE NANCAY RADIO TELESCOPE/

The 18-cm lines of the OH radical were monitored in C/1996 B2 (Hyakuta ke) with the Nancay radio telescope between 1 March and 18 May 1996. B esides providing regular measurements of the water production rate, th e C/1996 B2 campaign was useful to test and improve existing models of the OH density; excitation and transfer because the comet passed succ essively close to the Earth and close to the Sun. At the time of close st approach to Earth, a rough mapping was made by observing at offset positions several beam-widths (3.5') from the nucleus together with th e centre :, position. The OH line intensity at the centre was comparab le to those at offset positions, providing direct evidence for collisi onal quenching of the OH maser in the inner coma. After removing the G reenstein effect, The line profiles suggest a slight excess outgassing towards the Sun. We are able to detect the OH satellite lines at 1612 and 1721 MHz. A weak Zeeman splitting of the 1667 and 1665 MHz transi tions was observed :corresponding to an average line-of-sight magnetic field in the range +5 to +10 nT. (C) 1998 Elsevier Science Ltd. All r ights reserved.