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IAUC 8855: C/2007 N1; C/2006 VZ_13

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                                                  Circular No. 8855
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
URL http://www.cfa.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7440/7244/7444 (for emergency use only)


COMET C/2007 N1 (McNAUGHT)
     R. H. McNaught reports his discovery of a comet on CCD images
obtained with the 0.5-m Uppsala Schmidt telescope at Siding Spring
(discovery observation tabulated below); stacked images show the
object to be slightly diffuse with a diffuse tail about 10" long in
p.a. 240 deg.  Following posting on the Minor Planet Center's
'NEOCP' webpage, A. C. Gilmore writes that his CCD images taken on
July 11.64-11.70 UT with the Mt. John 1.0-m f/7.7 reflector show a
small, condensed coma and a short fan tail in p.a. 240 deg.  S.
Casulli notes that his CCD images taken on July 12.066 with a
0.40-m f/4.5 reflector at the Osservatorio Astronomico Vallemare di
Borbona show a coma nearly 12" in diameter, elongated toward p.a.
80 deg.

     2007 UT             R.A. (2000) Decl.       Mag.
     July 10.73325    1 42 19.69   + 1 10 08.4   17.7

The available astrometry, the following preliminary parabolic
orbital elements, and an ephemeris appear on MPEC 2007-N29.

     T = 2007 Sept. 7.236 TT          Peri. = 266.796
                                      Node  = 115.220   2000.0
     q = 2.28009 AU                   Incl. =   9.329


COMET C/2006 VZ_13 (LINEAR)
     M. L. Sitko, University of Cincinnati and Space Science
Institute; L. Beerman, University of Cincinnati; R. W. Russell, D.
K. Lynch, and R. Pearson, The Aerospace Corporation; H. B. Hammel,
Space Science Institute; and W. Golisch, Infrared Telescope
Facility (IRTF), NASA, report on observations made of comet C/2006
VZ_13 using the IRTF (+ BASS) on July 9 UT.  The comet exhibited a
continuum between 8 and 13 microns, on top of which a silicate
emission band from 8.5 to 12.2 microns was observed.  An underlying
blackbody, normalized to the continuum fluxes at 8.1 and 12.5
microns, yielded a mean grain temperature of 275 K (estimated
uncertainty +/- 5 K).  The derived temperature was 6 percent higher
than that of an equivalent radiative equilibrium blackbody at the
heliocentric distance of the comet.  The feature-to-continuum ratio
in the silicate band was 1.27.  The measured flux between 10.0 and
11.0 microns, using the 3".4 circular entrance aperture of BASS,
was 1.6 +/- 0.2 Jy (equivalent magnitude N = 3.5 +/- 0.1).
     Visual m_1 estimates by J. Gonzalez, Leon, Spain:  June 12.05
UT, 10.3 (25x100 bin.); 23.03, 9.4; 26.11, 8.8; July 4.91, 7.9
(7x50 bin.); 10.01, 7.3.

                      (C) Copyright 2007 CBAT
2007 July 12                   (8855)            Daniel W. E. Green

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