ANALYSIS OF POSS IMAGES OF COMET-ASTEROID TRANSITION OBJECTS 107P 1949 W1 (WILSON-HARRINGTON)/

We have analyzed the only two known images taken of Comet 107P = Aster oid (4015) Wilson-Harrington while it was a distinctly cometary object . The images reside on two Palomar Observatory Sky Survey (POSS) photo graphic plates taken ore 19 November 1949 UT and provide a unique way of studying the fading gasps of a dying comet. The comet appears as a streak, a tail is evident, but the coma is indistinguishable. A compar ison of the profiles of the streaks and the stellar PSF yielded no com a, implying the coma's scale height is small (upper limit of a few hun dred kilometers). Finson-Probstein modeling of the tail demonstrates t hat it is not a dust tail. If it were, the size of the particles would have to be tens to hundreds of micrometers in size (which contradicts the tail's blue color [vs. the Sun]) and they would have to have been released several weeks before the observations (which contradicts obs ervers' reports that the tail dissipated in a few days). Instead, we a re seeing CO+ and H2O+ fluorescence in a plasma tail. With this compos ition, the tail's blue hue and short lifetime are explained. The lag a ngle of the tail on the Image is about 15 degrees, larger than the '(t ypical)' for Type I tails, but the value is not implausible, We show t hat the deviation of the solar wind from radial need not have been aty pical to explain it, Pie have calibrated the relevant portions of the photographic plates and, from the surface brightness of the tail and a n estimate of its age, we have calculated a plausible maximum to the p roduction rate of H2O and CO during Wilson-Harrington's outburst: Q(H2 O) approximate to Q(CO) = 5 x 10(27) molecules sec(-1). Tile measureme nts indicate that CO is roughly as abundant as H2O on the dormant come t's nucleus. (C) 1997 Academic Press.