[IAUC] IAUC 8891: COMET 17P/HOLMES; C/2007 K21, C/2007 M10 [25139-2008/05-R1]

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                                                  Circular No. 8891
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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COMET 17P/HOLMES
     M. Drahus and L. Paganini, Max-Planck-Institut fuer
Sonnensystemforschung; and L. Ziurys, W. Peters, M. Soukup, and M.
Begam, Arizona Radio Observatory (ARO), report their monitoring of
comet 17P at millimeter wavelengths between Oct. 25.5 and 31.5 UT
with the ARO 12-m telescope on Kitt Peak.  Evolution of the
outburst was traced through the HCN(1-0) transition.  The following
integrals of the antenna temperature were obtained, with the three
hyperfine components summed, given in units of K km/s:  Oct. 25.54,
5.0 +/- 0.1; Oct. 27.58, 1.3 +/- 0.1; Oct. 28.38, 0.58 +/- 0.05;
Oct. 30.40, 0.62 +/- 0.05; Oct. 31.50, 0.39 +/- 0.06.  The gas-
expansion velocity, measured on the blue wing of the strongest HCN
line component, was fairly constant during the observations and
equal to 0.50-0.55 km/s.  The shapes and intensities of the HCN(1-0)
triplet on Oct. 25.54 and 27.58 confirm the presence of the "chunk",
and the isotropic "bubble" (cf. CBETs 1111, 1118), the "chunk"
being redshifted with respect to the nucleus.  Both features were
continually fading, likely due to photodissociation and because of
moving away from the beam center.  Since Oct. 28.38, the "chunk"
has not been visible in the line shapes, and the intensity of
HCN(1-0) has simultaneously stabilized; therefore, the measurements
obtained since then likely result from a regular (non-explosive)
post-outburst activity of the nucleus.  On Oct. 26.51, five lines
of CH_3OH were detected around 157 GHz, whose relative intensities
give a rotational temperature of 50 +/- 5 K.  The area of the
strongest line, 4(0,3)-4(1,4), was 0.78 +/- 0.04 K km/s.  Also
detected were CS(3-2) on Oct. 26.58 (1.48 +/- 0.04) and 29.38 (0.25
+/- 0.02); H_2CO(2(0,2)-1(0,1)) on Oct. 27.53 (0.08 +/- 0.04); and
H_2S(1(1,0)-1(0,1)) on Oct. 31.41 (0.13 +/- 0.02).  Sensitive 3-
sigma upper limits were obtained on CO(1-0) on Oct. 25.64 (< 0.2;
however, a positive residuum of 0.05 is visible) and 27.46, (<
0.08).  The half-power radius of the beam ranged from 19" to 36",
depending on the observed frequency.  The absolute calibration and
stability of the instrument is estimated to be better than 20
percent.


COMETS C/2007 K21 AND C/2007 M10 (SOHO)
     Additional Kreutz-sungrazing comets (cf. IAUC 8890) -- both of
mag about 7 and stellar, though C/2007 M10 appeared diffuse in C2
images:

 Comet        2007 UT      R.A.(2000)Decl.   Inst.  F    MPEC
 C/2007 K21   May  23.358   3 59.9  +18 50   C2     KB   2007-U23
 C/2007 M10   June 29.846   6 23.8  +20 53   C3/2   BZ   2007-U16

                      (C) Copyright 2007 CBAT
2007 November 6                (8891)            Daniel W. E. Green