[IAUC] IAUC 9107: C/2010 A4; P/2010 A1 [25139-2010/01-R1]

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                                                  Circular No. 9107
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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Phone 617-495-7440/7244/7444 (for emergency use only)


COMET C/2010 A4 (SIDING SPRING)
     On Jan. 12, G. J. Garradd reported his discovery of an
apparently asteroidal object on CCD images taken with the 0.5-m
Uppsala Schmidt telescope (discovery observation tabulated below);
after posting on the Minor Planet Center's 'NEOCP' webpage, Garradd
later reported the object being elongated about 10" in p.a. 150 deg
but with no clear tail in four 60-s stacked exposures.  Other CCD
astrometrists have also commented on the object's cometary
appearance, including W. H. Ryan (Magdalena Ridge Observatory,
2.4-m f/8.9 reflector, Jan. 13.35-13.38 UT), who noted a tail in
p.a. about 325 deg in R-band images.  E. Guido, Castellammare di
Stabia, Italy, reports that twenty co-added 120-s unfiltered
exposures taken by G. Sostero and himself remotely with a 0.25-m
f/3.4 reflector located near Mayhill, NM, U.S.A., on Jan. 13.4 show
a diffuse coma nearly 8" in diameter with a very weak central
condensation.  S. Foglia writes that thirty stacked 60-s images
taken by R. Holmes (Ashmore, IL, U.S.A., 0.61-m reflector, Jan.
13.5) show the object to be diffuse.

     2010 UT             R.A. (2000) Decl.       Mag.   Observer
     Jan. 12.72144   11 02 04.71   -27 10 15.5   18.7   Garradd

Further astrometry, the following preliminary parabolic orbital
elements, and an ephemeris are given on MPEC 2010-A76.

     T = 2010 Oct.  8.813 TT          Peri. = 272.446
                                      Node  = 346.731   2000.0
     q = 2.70743 AU                   Incl. =  96.846


COMET P/2010 A1 (HILL)
     Additional astrometry has show this comet (cf. IAUC 9104)
to be of short period; elements from MPEC 2010-A50:

     T = 2009 Aug.  9.353 TT          Peri. =  13.869
     e = 0.55136                      Node  =  47.080   2000.0
     q = 1.94218 AU                   Incl. =  10.265
       a =  4.32903 AU     n = 0.109426     P =   9.01 years

                      (C) Copyright 2010 CBAT
2010 January 14                (9107)            Daniel W. E. Green