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IAUC 5391: 1991o; 1991t

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                                                  Circular No. 5391
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM     EASYLINK 62794505

     Further observations of the splitting of the nucleus (cf. IAUC
5347) have been reported by S. M. Larson (Sept. 7, 9, Oct. 7, 8),
J. V. Scotti and T. Gehrels (Sept. 17, Oct. 2, 15, 16, Nov. 5), J.
Luu and D. Jewitt (Oct. 4-6), and R. H. McNaught (Oct. 5).
     Z. Sekanina, Jet Propulsion Laboratory, California Institute of
Technology, reports: "A solution based on 29 positional observations
of the two nuclei between Sept. 7 and Nov. 5 indicates that the
companion (the fainter nucleus) separated from the primary at 3.3 AU
from the sun, on 1991 Apr. 14.7 +/- 4.1 UT.  The separation velocity
is found to be higher than that for any other split comet: 15.00 +/-
0.93 m/s along the radius vector in the direction of the sun, 0.60
+/- 0.15 m/s in the direction perpendicular to the radius and toward
the direction from which the comet has come, and 0.23 +/- 0.03 m/s
in the direction of the comet's north orbital pole.  The secondary
has been subjected to a differential nongravitational deceleration
of 189 +/- 17 units of 10E-5 solar attraction and, in the terminology
introduced elsewhere for the split comets (Sekanina 1982, in Comets,
ed. L. L. Wilkening, Univ. Arizona, p. 251), it represents a
minor companion.  The solution satisfies the observations with a
mean residual of +/- 0".33.  The correlation between the deceleration
and the endurance that applies to most other split comets suggests
that the companion should disappear shortly.  The ephemeris
shows no major change in the configuration until around perihelion,
by which time the probability of the companion's survival is
virtually nil."

     Total visual magnitude estimates (cf. IAUC 5372):  Oct. 25.16
UT, 9.5 (H. Mikuz, Ljubljana, Yugoslavia, 0.20-m reflector); 28.19,
8.7 (J. Jahn, Bodenteich, Germany, 0.20-m reflector); Nov. 3.49, 9.2
(A. Hale, Las Cruces, NM, 0.41-m reflector); 6.25, 9.9 (A. Pereira,
Cabo da Roca, Portugal, 0.15-m reflector); 11.20, 10.1 (Mikuz);
12.52, 9.4 (C. S. Morris, Pine Mountain Club, CA, 0.26-m reflector);
16.55, 10.2 (R. Donner, Isla Vista, CA, 0.25-m reflector); 17.14,
10.6 (B. H. Granslo, Fjellhamar, Norway, 0.20-m reflector); 18.40,
10.1 (J. E. Bortle, Stormville, NY, 0.32-m reflector).

1991 November 21               (5391)             Daniel W. E. Green

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