CN, C2, AND DUST OBSERVED IN COMET P-GRIGG-SKJELLERUP FROM THE GROUND 8 HOURS AFTER THE GIOTTO ENCOUNTER

Comet P/Grigg-Skjellerup was observed with the 3.6m and 1.5m telescopes of ESO 8 hours after the encounter of Giotto with the comet. The CN and C2 production rates Q(CN) and Q(C2), have been derived from a spectrum obtained at the 1.5m telescope. We find log(Q(CN)) = 24.60 +/- 0.07 and log(Q(C2)) = 24.42 +/- 0.06. From a direct image of the comet, obtained by averaging 5 individual images taken at the 3.6m telescope through a special red wide-band filter, the distribution and content of the dust of comet P/Grigg-Skjellerup can be studied. The power exponent of the dependence of the azimuthally smoothed cometary intensity on projected distance rho equals -1.38. This low value may be caused by the influence of radiation pressure. The product geometric albedo x phase function x filling factor x projected distance (p PHI(alpha)f rho) amounts to 3.8cm. The values agree with measurements from previous apparitions. The results indicate that the dust to gas ratio of comet P/Grigg-Skjellerup is about three times lower than that of comet P/Halley.