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                                                  Circular No. 3465
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM     Telephone 617-864-5758

     E. Bowell, Lowell Observatory, communicates the following precise
position, measured by him from an exposure by H. Guetter with
the 1.5-m astrometric reflector at the U.S. Naval Observatory's
Flagstaff Station:

     1980 UT             R. A. (1950) Decl.
     Apr.  1.21104    10 22 37.41   +11 27 50.4

The comet's image is diffuse and uncondensed (in moonlight).

     Computations by Bowell, and also by P. Herget, Cincinnati,
confirm the general correctness of the parabolic orbit on IAUC 3461,
and that the comet is currently located 1.7 AU beyond Jupiter.
Bowell points out, however, that the comet will make a c1ose
approach to Jupiter in 1980 Dec., and that since it passes on the
inside of Jupiter's orbit the comet's orbit will become hyperbolic.
Computations by the undersigned suggest that if the orbit is currently
an osculating parabola, the closest approach to Jupiter will
be 0.24 AU, and that at the comet's perihelion passage in 1982 Mar.
e will have increased to 1.05 (q = 3.35 AU, 1/a = -0.015 AU**-1).

     B. Margon, R. A. Downes and P. Szkody, University of California
at Los Angeles, write that spectrophotometric and phptometric observations
of this object (IBVS 1630, IAUC 3462; R.A. = 15h35m44s, Decl. =
+19o01'.5, equinox 1950.0) made on ten nights in 1979-80 from Lick
and Kitt Peak Observatories reveal several extraordinary variations
synchronous with the 228-min period.  The equivalent widths of the
Balmer and He I 587.6-nm emission lines increase and decrease
smoothly by a factor of 2.5 during a 20-min period centered on the
40-min (full width) broadband eclipse but are roughly constant
throughout the rest of the orbit.  The He II 468.6-nm emission is
also relatively constant, except for a remarkable brief decrease (30
percent) in equivalent width of duration < 5 min, which has repeatedly
been observed to precede the center of the broadband eclipse
by 5 +/- 1 min.  Variable-strength Na D and Mg b absorptions, reaching
maximum strengths of 0.1- and 0.2-nm equivalent width, are also
detected.  The absorption is present on less than half of the spectra,
and its variation in strength shows no obvious phase dependence.

1980 April 3                   (3465)              Brian G. Marsden

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