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 comet 273P/PONS-GAMBART ( =1827 M1 = 2012 V4 )

Photometric data obtained by use of FOCAS-II software

                                   10x10  20x20  30x30  40x40  50x50  60x60   SNR   SB   COD

OBJECT        DATE       TIME        +/-    +/-    +/-    +/-    +/-    +/-     N  FWHM  CAT

------------  ---------- --------  -----  -----  -----  -----  -----  -----  ----  ----  ---

273P          01/04/2013 23:55:00  15.70  14.81  14.30  13.95  13.70  13.51  11.8  17.5  B96

273P          01/04/2013 23:55:00*  0.05   0.05   0.05   0.06   0.07   0.06     5   3.8  USN

273P          02/04/2013 23:48:41  15.91  14.97  14.43  14.07  13.83  13.66  10.4  17.2  B96

273P          02/04/2013 23:48:41*  0.10   0.06   0.06   0.05   0.04   0.04     5   3.8  USN

273P          07/04/2013 02:16:03  16.38  15.63  15.15  14.80  14.54  14.34  14.5  18.4  B96

273P          07/04/2013 02:16:03*  0.07   0.07   0.06   0.05   0.05   0.04     5   3.1  USN

COMET         UTC                   DELTA    R    APER    Mag   AfRho   +/-   Log   Obs

------------  -------------------   -----  -----  -----  -----  -----  ----  -----  ---

273P          01/04/2013 23:55:00    1.26   1.91  21.84  14.70     74     6  1.869  B96

273P          02/04/2013 23:48:41    1.27   1.93  21.68  14.86     66     6  1.817  B96

J.L.Pons (Florence Italyu) discovered this comet on 1827 june 21.04. An independent discovery was made by J.F.A. Gambart (Marseille, France) just minutes later. Few physical discriptions were published for this comet. Pons was the most profilic observer, measuring 3 additional positions in june and a total of 17 in july.. Pos said that the comet was extremely faint when Pons observed this comet for at last on july 21.

273P/Pons–Gambart, also called Comet Pons-Gambart, is a short-period comet .  It has a 186 year orbit. It fits the classical definition of a Halley-type comet with (20 years < period < 200 years). It was lost and was not recovered until November 7, 2012, when amateur astronomer Rob Matson discovered a comet,  (Newport Coast, California, US) in SWAN imagery from Nov 2012.  And it was identified that the pre-recovery short-arc orbital calculations for Pons-Gambart were completely wrong because the comet only had a 1-month observation arc with poor data.  Terry Lovejoy (Thornsland, Queensland, Australia) managed to capture the comet on Nov 29.4 UT 2012 from ground-based, apparent diameter around 2', 10th magnitude. On Nov 30.4 UT 2012, Robert H. McNaught from Siding Spring confirmed the discovery through the 0.5-m Uppsala Schmidt. A 6' tail in P.A. 101° was also identified. However, it was not the end of the story. Maik Meyer (Limburg, Germany) suggested the similarity between the orbit of the new comet and that of D/1827 M1 (Pons-Gambart). Syuichi Nakano (Somoto, Japan) attempted to establish the linkage, however, the residual was enormous provided that the orbital period is around half of a century. The comet was thereby designated C/2012 V4 ( CBET 3321 ) . More observations proved that the period is actually much longer than previously expected.

Finally MPC 2012-X14 announced the comet as 273P/2012 V4 (Pons-Gambart).

The orbital elements, like those on MPEC X02, assume that C/2012 V4 is a return of D/1827 M1 (Pons-Gambart).  Whereas that earlier orbit assumed that there were two missed returns between 1827 and 2012, the above orbit assumes no missed returns.  The much longer period was suggested by the current observations not being well fit to orbital periods of ~62 and ~94 years.  Noting the obvious discordance between the two E27 observations on Nov. 29, the semimajor axis fit by the 2012 observations alone is at least 26 AU, discounting the two- and three-missed revolution solutions.  At the present time, the solution presented here is believed to be correct, as the fit of the bulk of the 1827 observations (known to be grossly inaccurate by modern standards) is far better than earlier attempts with shorter orbital periods.  There is a slight systematic trend in the current residuals, which may be related to observation weighting.  Continued observation is clearly desirable.