Activity of Comet Tabur (C/1996 Q1) during September 12-17, 1996

We have obtained and analyzed narrow (CN and continuum) and broadband (B, V , R) CCD images and long-slit spectra of the coma of Comet C/Tabur (1996 Q1 ), which is a fragment of a split comet together with C/Liller (1988 Al). T he observations were taken on Sept. 12-17, 1996, before its first perihelio n passage. A detailed structural analysis of the CN images revealed the pre sence of a double jet structure, shells, and a higher emission on the daysi de of the comet that can be attributed to an active area. All of these stru ctures in CN have no counterparts on the dust. The broadband images showed the same double jet structure with an overimposed dust tail. The CN and Ct production rates, as well as the dust production rate deduced from the cust omary Afp, show a steady increase during the five days the comet was monito red, reaching a maximum on Sept. 14. The surface brightness profiles of the continuum, either from the images or from the long-slit spectra, show a ve ry steep gradient (1.67 less than or equal to m less than or equal to 2.25) at projected radial distances (rho) shorter than 3200 km in the Sun direct ion, whereas at p r 3200 km all continuum profiles can be well fitted with m approximate to 1 in log B - log rho representation. The shape of the brig htness profiles follows the same pattern during five consecutive days, unli ke the flux, which differs from Sept. 13 to 14 and from Sept. 14 to 16. Fur ther analysis of the reflectivity variations proves that the reflectance of the dust behaves differently in the Sun and in the tail directions. The co ntinuum light scattered from the dust in the coma of Comet Tabur is bluest at rho similar to 1800 km east photocenter (i.e., Sun direction), whereas w estward the reflectivity of the dust can be regarded as constant at every r ho. The reflectivity variations are much the same in all spectra of Comet T abur on Sept. 13-16. In principle, the data can be interpreted as the progr essive destruction (either by fragmentation and/or by ice sublimation) of t he grains in the dust coma of the comet. As Comet Tabur is probably a fragm ent of a split comet (Marsden 1996a,b), it might have released fresh, less processed material coming from the interior of the nucleus. (C) 2001 Academ ic Press.