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IAUC 8342: C/2001 Q4

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                                                  Circular No. 8342
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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COMET C/2001 Q4 (NEAT)
     J. L. Wilde and M. L. Sitko, University of Cincinnati; and D.
L. Kim and R. W. Russell, The Aerospace Corporation, report 3-13-
micron spectrophotometry of comet C/2001 Q4 obtained on May 14.1 UT
with the Mt. Lemmon 1.5-m University of Minnesota telescope (+
Aerospace Broadband Array Spectrograph System; 8".5 aperture; 51"
chop throw; integration times 20 min on the comet and 10 min on the
reference star, beta Gem):  "A smooth comet continuum was seen to
rise from 3 to 5 microns and from 7.1 to 8.4 microns, a little
above the blackbody (about 310 +/- 5 K) that was fit to the
continuum points on either side of the strong, structured silicate
feature seen from 8.4 to 12 microns.  This temperature is
consistent with the temperature reported by Woodward et al. (IAUC
8339) but is dependent upon assumptions of where the silicate grain
emissivity becomes much less than the emissivity of the (assumed)
gray-body grains that emit the underlying contiuum.  The grain
temperature is about 9 percent higher than that of an equilibrium
blackbody at the heliocentric distance of the comet.  The continuum
was fairly flat beyond 12 microns.  The rising flux above the
blackbody from 7 microns towards 3 microns may be due to scattered
sunlight, thermal emission from grains with a mix of temperatures
and optical properties, or both.  Structure is seen in the silicate
feature, but at slightly different wavelengths from those reported
by Woodward et al.  Here, emission peaks are seen at 10.5 and 11.2
microns, with no feature at 9.3 microns.  The silicate-feature-to-
continuum ratio was about 1.65, also consistent with the report by
Woodward et al.  With our aperture, the comet has narrowband (about
0.25 micron) magnitudes and combined random errors (due to
calibration star and comet) of [3.5 microns] = 5.44 +/- 0.09, [4.5
microns] = 3.44 +/- 0.03, [5 microns] = 2.96 +/- 0.03, [8 microns]
= -0.10 +/- 0.01, [10.5 microns] = -1.65 +/- 0.01, and [12 microns]
= -1.72 +/- 0.03.  The combined comet-and-calibration-star
systematic intensity uncertainty is estimated at about 5 percent.
The ratio of this brightness to that of Woodward et al. is
consistent with a roughly linear dependence on aperture, or a 1/R
radial grain-density dependence from the comet nucleus."
     Visual total-magnitude and coma-diameter estimates: Apr. 27.54
UT, 4.2, 11' (A. Pearce, Nedlands, W. Australia, 8x40 binoculars);
May 6.25, 3.0, - (S. J. O'Meara, Volcano, HI, naked eye); 9.19,
2.9, 17'.5 (C. S. Morris, Lake Tahoe, CA, 10x50 binoculars; 7.25-
deg tail); 10.83, 2.9, 27' (R. Haver, Frasso Sabino, Italy; 10x50
binoculars; tail about 5 deg long in p.a. 105 deg); 14.87, 3.6, 22'
(K. Hornoch, Lelekovice, Czech Republic, 10x50 binoculars; 3.5-deg
tail in p.a. 105 deg); 17.88, 3.7, - (M. Meyer, Kelkheim, Germany,
naked eye); 19.24, 4.0, 10' (C. E. Spratt, Victoria, BC, 7x50

                      (C) Copyright 2004 CBAT
2004 May 19                    (8342)            Daniel W. E. Green

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