[IAUC] IAUC 9206: C/2011 H1 [25139-2011/04-R1]

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                                                  Circular No. 9206
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
New postal address:  Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
CBATIAU en EPS.HARVARD.EDU           ISSN 0081-0304
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Prepared using the Tamkin Foundation Computer Network


COMET C/2011 H1 (LEMMON)
     Alex R. Gibbs reported his discovery of an apparently
asteroidal object (discovery observation tabulated below) that he
suspected might show slight cometary appearance (with some slight
diffuseness in p.a. 135 deg), from CCD images taken with the Mt.
Lemmon 1.5-m reflector.  The object was posted with Gibbs'
preliminary designation on the Minor Planet Center's NEOCP webpage,
after which a couple of other CCD astrometrists independently noted
some diffuseness; though the object was given the minor-planet
designation 2011 GK_71 on MPEC 2011-H41 based on a series of one-
night astrometry (Apr. 14) from Spacewatch, it is here designated
comet C/2011 H1 because the Apr. 26 observations were the discovery
observations that allowed the other astrometry to be connected.  G.
Sostero and E. Guido, observing remotely on Apr. 27.5 UT with a
0.15-m f/7 refractor (eight stacked, unfiltered 300-s exposures,
obtained using the Tzec Maun Observatory near Moorook, Australia),
found the object to be slightly diffuse (its FWHM nearly twice that
of nearby field stars of similar brightness; total red mag 19.1).
R. S. McMillan, J. V. Scotti, and M. L. Terenzoni stacked six 90-s
R-band exposures that were obtained with the Steward Observatory
Bok 2.3-m f/3 reflector (+ 90Prime CCD camera) during Apr. 29.256-
29.301 in 1".3 seeing; the resulting image of the object appears
nearly stellar, but it shows a coma diameter of 5" and a tail 9"
long in p.a. 111 deg.  Scotti adds that he stacked twelve frames
obtained during Apr. 30.321-30.374 with the Spacewatch II 1.8-m
telescope to find that the nearly stellar object shows a faint 9"
coma and a very faint tail 0'.20 long in p.a. 119 deg; he also
notes that review of the Apr. 14 Spacewatch observations
(identified by the MPC staff, subsequent to Gibbs' discovery but
prior to issuing MPC 2011-H41) now shows little or no cometary
appearance (which Scotti explains is why he did not report it as
cometary when he viewed that image on Apr. 14).

     2011 UT             R.A. (2000) Decl.       Mag.   Observer
     Apr. 26.29827   14 10 31.04   -23 27 01.3   19.7   Gibbs

The following preliminary parabolic orbital elements by G. V.
Williams are from 36 observations, Mar. 29-Apr. 30, and include
Mar. 29 Catalina observations identified by Gibbs (which appear
with additional astrometry and an ephemeris on MPEC 2011-J24).

     T = 2006 Jan. 31.1303 TT         Peri. = 100.9311
                                      Node  =  35.5786  2000.0
     q = 6.912174 AU                  Incl. =  73.9837

                      (C) Copyright 2011 CBAT
2011 May 5                     (9206)            Daniel W. E. Green