[IAUC] IAUC 9104: C/2010 A1; 81P [25139-2010/01-R1]

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                                                  Circular No. 9104
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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COMET C/2010 A1 (HILL)
     R. E. Hill, Lunar and Planetary Laboratory, reports his
discovery of a comet on CCD images taken with the Catalina 0.68-m
Schmidt reflector (discovery observation tabulated below),
describing the object from co-added exposures in 2"-4" seeing as
having a nuclear condensation about 4"-5" across with a 12"-15"-
radius coma beyond that and no obvious tail (but a slight east-west
elongation) in moonlight; his follow-up images in thin haze on Jan.
7.24-7.25 UT show a similar appearance but with a short, fan-shaped
tail 20"-30" long in p.a. about 270 deg.  Four co-added images
obtained by E. C. Beshore with the Mt. Lemmon 1.5-m reflector on
Jan. 6.5 showed a very faint tail perhaps 15" long in p.a. 270 deg.
Following posting on the Minor Planet Center's 'NEOCP' webpage,
other CCD astrometrists have noted the object's cometary appearance.
Y. Ikari (Moriyama, Shiga-Ken, Japan, 0.26-m f/7 reflector, Jan.
6.6) measured a coma diameter of 0'.2.  P. Birtwhistle (Great
Shefford, Berkshire, England, 0.40-m f/6 Schmidt-Cassegrain
reflector, Jan. 7.1) found a diffuse coma of size 15" x 22",
elongated in p.a. 310 deg, with a weak condensation offset to the
southeast (the brightest part of the surrounding coma is 6" x 12"
and extends in p.a. 50 deg and 230 deg).  H. Sato (Ota-ku, Tokyo,
Japan, remotely using a 0.25-m f/3.4 reflector of the RAS
Observatory, near Mayhill, NM, U.S.A., Jan. 7.2) finds a 20" coma
elongated toward p.a. 110 deg.  W. H. Ryan (Magdalena Ridge
Observatory, 2.4-m f/8.9 reflector, Jan. 7.3) remarked on a
distinct coma.

     2010 UT             R.A. (2000) Decl.       Mag.   Observer
     Jan.  6.46381    9 11 26.44   +33 08 34.6   17.6   Hill

Further astrometry, the following preliminary parabolic orbital
elements, and an ephemeris are given on MPEC 2010-A31.  It is
possible that the comet is of short period.

     T = 2010 June 24.055 TT          Peri. = 219.047
                                      Node  =   6.140   2000.0
     q = 1.02031 AU                   Incl. =  11.782


COMET 81P/WILD
     Visual total-magnitude estimates:  Nov. 24.17 UT, 10.5 (J. J.
Gonzalez, Leon, Spain, 20-cm reflector); Dec. 12.16, 10.3 (Gonzalez);
29.21, 10.3 (M. Meyer, Limburg, Germany, 15-cm refractor).

                      (C) Copyright 2010 CBAT
2010 January 7                 (9104)            Daniel W. E. Green