CCD imaging and photometry of 46P/Wirtanen during October 1996

During the period of 96 Oct. 7.16 to Oct. comet P/Wirtanen was observed with our CCD system at the 154 cm Catalina Observatory telescope at a heliocentric distance near 2.1 AU. The comet exhibited a coma of about 7 in in diameter with a tail of he observed B, V and R magnitudes within a 9.3 in diameter aperture were 19.94, 19.11 and respectively: The large majority of our observations were carried out with a filter combining the V and R passbands (V+R). The average V+R magnitudes for Oct. 7.16, 8.14, 9.12 and 10.15, respectively, were 18.91, 18.87, 18.87 and 18.86. The data did not allow the extraction of a lightcurve but hopefully can in conjunction with other observations to cpn gin the comet's rotation period. An attempt to sep nucleus contribution from the coma resulted in an upper limit to the nuclear magnitude of approximate to 20.6 in V+R at a phase of 26 degrees or approximate to 19.6 at 0 degrees phase angle. ts in an upper limit of 1.2 km for the comet's radius assuming a geometric albedo of 0.04. Calculating the Af rho yielded a value of 7 cm which is a factor of 170 smaller than P/Halley at a comparable heliocentric distance and phase angle. Making the simple assumption that the comet's activity is proportional to its surface area makes the surface area of Wirtanen about 2.4 km(2), equivalent to an effective radius of approximate to 0.44 km. (C) 1997 Published by Elsevier Science Ltd. All rights reserved.