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IAUC 8742: C/2006 Q1; 73P

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IAUC number

                                                  Circular No. 8742
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
URL http://cfa-www.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7440/7244/7444 (for emergency use only)

    R. H. McNaught reports his discovery of a comet (discovery
observation tabulated below) on CCD images obtained with the 0.5-m
Uppsala Schmidt telescope in the course of the Siding Spring Survey,
noting a soft image with an apparent coma diameter of about 8" in
4" seeing; his observations on Aug. 21.73 and 21.78 UT showed the
comet to be again slightly diffuse, with deep exposures showing a
diffuse condensation and a 20"-diameter coma.  CCD images taken at
low altitude by J. Young with the 0.61-m reflector at Table
Mountain on Aug. 23.5 show a round, 8" coma with a hint of central
condensation, with no suggestion of any tail in long exposures.

     2006 UT             R.A. (2000) Decl.       Mag.
     Aug. 20.74130    5 24 12.81   -25 25 43.5   17.8

The initial astrometry and a very preliminary orbit were published
on MPEC 2006-Q22.  Additional astrometry and revised parabolic
orbital elements [T = 2008 June 29.669 TT, q = 2.70330 AU, Peri. =
345.338 deg, Node = 199.406 deg, i = 58.994 deg (equinox 2000.0)]
appear on MPEC 2006-Q50.

     M. L. Sitko, University of Cincinnati and Space Science
Institute; R. W. Russell, D. K. Lynch, and R. Ford, Aerospace
Corporation; H. B. Hammel, Space Science Institute; and W. Golisch
and P. Sears, Infrared Telescope Facility (IRTF), NASA, report on
post-perihelion observations made of comet 73P's component 'C'
using the IRTF (+ BASS) on Aug. 5, 7, and 8 UT.  The comet
exhibited a continuum between 3 and 13 microns, on top of which a
silicate emission band from 8.5 to 12.2 microns was observed.  The
flux observed on all three days was approximately the same, to
within 10 percent.  An underlying blackbody, normalized to the
continuum fluxes of the averaged spectra at 8.1 and 12.5 microns,
yielded a mean grain temperature of 272 K (estimated uncertainty
+/- 5 K).  The derived temperature was 10-11 percent higher than
that of an equivalent blackbody at the heliocentric distance of the
comet.  The feature-to-continuum ratio in the silicate band was
1.19, smaller than that previously reported for this fragment from
pre-perihelion observations (IAUC 8701 and 8717).  The measured
flux between 10.0 and 11.0 microns, using the 3".4 circular
entrance aperture of BASS, was 0.28 +/- 0.03 Jy (equivalent
magnitude m_N = 5.4 +/- 0.1).

                      (C) Copyright 2006 CBAT
2006 August 29                 (8742)            Daniel W. E. Green

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