FIRST IMAGES OF A COMET WITH ADAPTIVE OPTICS

Using the ADONIS adaptive optics system at ESO (La Silla, Chile), on 8 March 1996, we made the very first observation of a comet with adapti ve optics. Comet C/1996 B2 (Hyakutake) has been imaged in the near-inf rared (J, H, K bands at 1.2, 1.6 & 2.2 mu m respectively). The achieve d spatial resolution of approximate to 0.2 '', has allowed us to isola te two distinct dust-colour regions in the immediate neighbourhood of the cometary nucleus. On a [J-H] colour index map, a bluer region has been detected in the sunward-facing hemisphere, while a redder one is located symmetrically in the anti-solar direction. The major dust comp onent in the coma remains silicates. These new observations should hel p to constrain the current models for dust components in comets. They clearly demonstrate the feasibility of observing comets with adaptive optics systems. Future observations of comet Hale-Bopp should greatly benefit from this new technique. (C) 1998 Elsevier Science Ltd. All ri ghts reserved.