Comet 1989x (SMM 10)

O. C. St. Cyr, High Altitude Observatory, reports his discovery of the tenth probable sungrazing comet recorded by the coronagraph on the Solar Maximum Mission. The following measurements were made by J. Burkepile and A. Stanger, High Altitude Observatory, and the reduction was by D. Pitone and B. Twambly of the SMM Flight Dynamics Facility at NASA Goddard Space Flight Center. The measurements refer to the 'head' (i.e., the sunward end of the bright cometary tail), and radial distance and p.a. are believed accurate to +/- 0.1 solar radius and +/- 0.1 deg, respectively. 1989 UT R.A. (1950) Decl. Sept.28.696 12 13.31 - 2 10.3 28.713 12 13.91 - 2 10.3 28.724 12 14.35 - 2 09.2 28.760 12 15.76 - 2 06.8 28.771 12 16.12 - 2 06.6 28.776 12 16.34 - 2 05.9 28.788 12 16.90 - 2 05.0 SMM 10 is one of the brighter SMM comets, and in comparison to the others it has a large tail (longer than a solar diameter). As was the case with SMM 5 (IAUC 4668) the tail has an unusual shape, with a conspicuous bulge on the northern side (i.e., toward the solar equator) near the end. Also like SMM 5, there appears to be a wispy structure extending further north and sunward from this bulge, and the wispy structure appears to track with the comet in at least three images. SMM 10 was probably brighter than mag -4, and the head disappeared into the occulting disk after Sept. 28.792 UT. The comet was not seen to reappear, but the data stream was interrupted during Sept. 28.85-29.02 UT. The following parabolic orbital elements, derived by B. G. Marsden, Center for Astrophysics, on the assumption that the perihelion direction is that of the Kreutz sungrazers, satisfy all the above positions within 1'.2: T = 1989 Sept. 28.855 ET, Peri. = 87.50, Node = 8.94, Incl. = 144.76 (equinox 1950.0), q = 0.00476 AU. The assumption that the comet's original orbit is the same as that of comet 1963 V (Marsden 1989, A.J., in press) yields a slight systematic trend with residuals up to 1'.7 and the elements: T = 1989 Sept. 28.857 ET, Peri. = 87.25, Node = 8.52, Incl. = 144.58 (equinox 1950.0), q = 0.00487 AU.