CCD photometry of comet 46P/Wirtanen

CCD observations of 46P/Wirtanen obtained in February 1992, when the comet was at a postperihelion heliocentric distance of R = 1.93AU are analysed. At this time the comet possessed a weak dust coma extending > 5000 km from the nucleus. The observed brightness distribution reveals no sign of any central nucleus, and results in a firm upper limit to the radius of the nucleus of re<2.8km (assuming an albedo of 4%), similar to that found by Jorda and Rickman (Planet. Space Sci. 43, 575–579, 1995) and consistent with the reported detection by Boehnhardt et al. (Astron. Astrophys. 1997, in press). Wirtanen was also searched for in June 1995 and August 1995, but this was unsuccessful in detecting the comet. An upper limit to the nucleus size of 8.2 km was obtained from these data, consistent with the values above.