[IAUC] IAUC 9212: C/2011 L1; T Pyx [25139-2011/04-R1]

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                                                  Circular No. 9212
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 L1 (McNAUGHT)
     Robert H. McNaught reports his discovery of a comet (discovery
observation tabulated below) on CCD images taken with the 0.5-m
Uppsala Schmidt telescope at Siding Spring; on the discovery
images, the object appears nearly asteroidal with a 10" coma and a
1'.4-long narrow tail in p.a. 225 deg.  McNaught's images from June
3.4-3.6 show a tail 0'.7 long in p.a. 220-225 deg; he adds that the
comet's head merges into the tail, making a small aperture
essential to define the center of light for astrometry.  On June
6.4, McNaught found total mag 16.2 and a 0'.6 tail in p.a. 218 deg,
again noting the difficulty in determining the astrometric center
of light, suggesting that most measures will be biased down the
tail to some extent.  After posting on the Minor Planet Center's
'NEOCP' webpage, other CCD astrometrists have commented on the
object's cometary appearance.  Three images taken by J. D.
Armstrong, A. N. Martin, M. Micheli, M. E. Schindler, and S. H.
Spear with the 'Faulkes Telescope South' 2.0-m f/10 reflector on
June 3.52-3.56 show a 7" elliptical coma elongated toward the tail,
which itself was 1'.5 long in p.a. 213 deg.  Thirty stacked 60-s
images taken by R. Holmes (Ashmore, IL, USA, 0.61-m f/4 astrograph,
June 4.2) show an 8" round coma and a 25" tail in p.a. 230 deg
(measured by S. Foglia and T. Vorobjov).  Foglia adds that stacked
images taken remotely on June 4.64-4.67 by S. Baroni, L. Buzzi, P.
Concari, G. Galli, M. Tombelli, and himself with a 0.18-m f/2.8
reflector at the Tzec Maun Observatory near Moorook, Australia,
show a 10" round coma (total red mag 16.2-16.6) and a 120" tail in
p.a. 215 deg.

     2011 UT             R.A. (2000) Decl.       Mag.   Observer
     June  2.63479   16 08 14.08   -34 30 36.5   16.9   McNaught

The available astrometry, the following preliminary parabolic
orbital elements by G. V. Williams, and an ephemeris appear on MPEC
2011-L26.

     T = 2011 Jan.  1.129 TT          Peri. = 301.300
                                      Node  = 251.426   2000.0
     q = 2.41987 AU                   Incl. =  70.862


T PYXIDIS
     Additional visual magnitude estimates (cf. IAUC 9207):  May
7.059 UT, 6.7 (R. Salvo, Montevideo, Uruguay); 8.993, 7.2 (W.
Souza, Sao Paulo, Brazil); 12.045, 6.6 (Salvo); 18.973, 7.2
(Salvo); 26.000, 7.3 (Salvo).

                      (C) Copyright 2011 CBAT
2011 June 6                    (9212)            Daniel W. E. Green