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IAUC 5670: 1992t

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                                                  Circular No. 5670
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

     Observations in mid-November show that ephemerides from the
gravitational orbital elements on IAUC 5636 (by B. G. Marsden, utilizing
the 1862 Oct. observations) and on MPC 21081 (by D. K. Yeomans, utilizing
the 1862 July-Sept. observations) were both running off by as much as
15" in declination, the truth being roughly midway in between.  As
anticipated, gravitational solutions now completely fail to link the
apparitions.  The nongravitational solution below, from MPC 21235,
satisfies 383 observations with a mean residual of 1".3 and removes much
of the systematic effect, but the residual trend in 1862 Oct. is still in
excess of 10" in both R.A. and Decl.  The computed perihelion time in
1737 is about 0.5 day too early.

                    Epoch = 1992 Dec.  4.0 TT
     T = 1992 Dec. 12.3243 TT         Peri. = 153.0016
     e = 0.963589                     Node  = 139.4441  2000.0
     q = 0.958216 AU                  Incl. = 113.4266
       a = 26.316841 AU    n = 0.0073005    P = 135.005 years

Nongravitational parameters are A1 = -0.00079 +/- 0.00002, A2 = -0.00266
+/- 0.00007.  The new solution also satisfies the following pre-recovery

     1992 UT             R.A. (2000) Decl.        m1    Observer
     Jan.  3.07847   10 00 08.38   +42 59 08.0   17.5   Haver
           3.09184   10 00 07.84   +42 59 16.0            "
           7.08767    9 56 32.45   +43 56 49.2   18     Kohoutek

R. Haver (Cima Ekar).  0.4-m f/2.5 Schmidt.  Measurers A. Boattini and
   M. Tombelli.  Communicated by G. Forti.  Very weak images; stellar
L. Kohoutek (Calar Alto).  0.8-m Schmidt.  Close to plate limit;
   evidently some interference from cirrus clouds.

     Using computations by the undersigned and also by G. Waddington
(Oxford University), G. Kronk (Troy, IL) has confirmed the likelihood
of the -68 comet as a good candidate for P/Swift-Tuttle and has noted
that the only other viable candidate is the comet of +188.  He suggests
that the observations restrict the perihelion dates to the ranges
-68 July 27-28 and +188 July 5-Aug. 2 (with a most likely date of July 15).

1992 December 5                (5670)              Brian G. Marsden

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