NUCLEUS PROPERTIES OF P SCHWASSMANN-WACHMANN-1/

Time series photometric measurements are presented of comet P/Schwassm ann-Wachmann 1 at a heliocentric distance of 5.886 AU when the comet p ossessed an extensive coma. The light curve shows a modulation caused by the rotation of the nucleus. The rotation period is considerably sh orter than the 5 day period found by Whipple [AJ, 85, 305 (1980)] and we find substantial evidence that the nucleus may be in a complex spin state characterized by two periods 14.0 and 32.3 hr. Models of the ra te at which the rotational light curve range decreases as a function o f the amount of coma in the aperture have determined that the projecte d maximum to minimum axis ratio of the comet is 2.6 and that the produ ct of the albedo times the rotationally averaged nucleus radius size, p(R)R(N)2 is 9.5 +/- 0.3 km2. Assuming a minimum geometric albedo of p (R) = 0.04, the maximum projected average nucleus radius is R(N) = 15. 4 +/- 0.2 km, which is only 44% of the size estimated by Roemer [Mem. Soc. Roy. Sci. Liege, 13, Ser. 5, 23 (1966)]. However, using the albed o determined by Cruikshank & Brown [Icarus, 56, 377 (1983)] of p = 0.1 3, the nucleus radius is only R(N) = 8.6 +/- 0.1 km. Because of the un known nucleus orientation, these will be upper limits to the nucleus s ize. It appears that the nucleus of P/Schwassmann-Wachmann 1 is not th e large nucleus that it has been believed to be for nearly 40 yr.