OBSERVATIONS OF COMET P FAYE-1991-XXI WITH THE PLANETARY CAMERA OF THE HUBBLE-SPACE-TELESCOPE/

Comet P/Faye 1991 XXI (1991 n) was observed with the planetary camera (PC) of the Hubble Space Telescope (HST) between October 29 and Novemb er 21, 1991, when its geocentric distance was in the range 0.52-0.67 A U. The resulting high resolution-a single PC pixel projected to a dist ance of similar to 20 km at the comet-made it possible to clearly disc riminate the nucleus and to study the dust coma within similar to 100 km from the nucleus. The spherical aberration which affected the early operation of the HST has severely complicated the analysis and image restoration using the Richardson-Lucy method has failed to give satisf actory results, The coma is dominated by the point spread function (PS F) of the nucleus up to a radial distance of similar to 100 km and can not be recovered, Beyond, it is affected by the spherical aberration u p to approximately 750 km and was analyzed by comparison with a grid o f models convolved with appropriate PSFs. Beyond 750 inn, it remains u naffected and can be studied directly. From the outer to the innermost regions, the coma presents an elongated shape which may be explained either by an active source on the nucleus or, more likely, by a projec tion effect of the dust tail, if this second interpretation is correct , then the temporal evolution of the comet is very slow and smooth, su ggesting an extended source of dust on the nucleus, The dust productio n rate, corrected for the projection effect of the tail, amounts to 12 5 kg sec(-1). (C) 1996 Academic Press, Inc.