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IAUC 4234: 1808 III; AM Her

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                                                  Circular No. 4234
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 617-495-7244/7440/7444

     L. Kresak, Astronomical Institute, Slovak Academy of Sciences,
writes that the comet observed solely by J.-L. Pons at Marseilles
during 1808 Feb. 6-9 was apparently P/Grigg-Skjellerup, which is
therefore being given the above Roman numeral designation.  On the
assumption that the nebulae shown in the drawing in A.N. 7, 114
(1829) are M10 and M12 and that the comet is closer to the latter
(as the drawing is said to be 'renverse'), Kresak derives the
following position (which is evidently uncertain by several arcmin):

              1808 UT           R.A. (1950.0) Decl.

              Feb.  9.22       16 45.0      - 1 26

He notes that this position is in perfect agreement with a backward
integration performed by N. A. Belyaev et al. on the assumption
of constant nongravitational effects and a Delta-T adjustment of
less than 2 days, the resulting elements being:

           T = 1808 Mar. 17.10 ET
       Peri. = 193.55                    e =   0.7437
       Node  =  17.84   1950.0           a =   2.8541 AU
       Incl. =   3.49                    n =   0.20441
           q =   0.7315 AU               P =   4.82 years

The computed motion during 1808 Feb. 6-9 (-7 deg in declination, -15 deg
in solar elongation) is not inconsistent with Pons' statement that
the comet was moving rather rapidly to the south and the absence
of subsequent observations.  The great size of the coma (estimated
by Pons at almost 1 deg across) is not unreasonable, for the comet
would have been at geocentric distance Delta = 0.12 AU.  Kresak adds
that the above position is ~ 1 deg from the line of variation
corresponding to computations by A. Carusi et al. on the assumption of
zero nongravitational effects.  In view of the encounters with
Jupiter in 1881, 1845 and 1809, the positional residuals seem more
than satisfactory, and the identification appears to be certain.

     Visual magnitude estimates: Apr. 22.88 UT, 15.2 (C. Mendelson,
Wise Observatory); 27.91, 14.5 (M. Verdenet, Bourbon-Lancy,
France); May 29.0, 13.4 (A. Mizser, Budapest, Hungary); June 3.93,
14.2 (R. Monella, Covo, Italy); 4.89, 14.1 (Monella); 5, 13.5-14.4
(Mendelson; variable); 7.94, 13.5 (Monella); 9.0, 12.3 (Mizser).

1986 July 22                   (4234)              Brian G. Marsden

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