[IAUC] IAUC 8889: COMET 17P/HOLMES; C/2007 L12, C/2007 L13,, C/2007 M4 [25139-2008/05-R1]

Vie Nov 2 21:41:03 ART 2007

                                                  Circular No. 8889
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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COMET 17P/HOLMES
     D. Schleicher, Lowell Observatory, obtained eight sets of
narrowband photometry of comet 17P/Holmes on Nov. 1 (r = 2.47 AU)
using the Hall 1.1-m telescope at Lowell Observatory.  Projected
aperture radii ranged from 14500 to 120200 km, and derived
production rates exhibited large trends with aperture size for all
species -- with the highest values always at the largest apertures,
consistent with a slowly decreasing rate of overall activity since
the initial outburst.  Production-rate ranges for each species are:
log Q(OH) = 29.60-29.80; equivalent log Q(water; vectorial) =
29.54-29.74; log Q(NH) = 27.65-27.89; log Q(CN) = 27.26-27.51; log
Q(C_2) = 27.33-27.61; log Q(C_3) = 26.64-26.87; log [Af(rho)] (526
nm) = 5.13-5.74 (cf. IAUC 7342).  The resulting abundance ratios
indicate that comet 17P has 'typical' composition (based on A'Hearn
et al. 1995, Icarus 118, 223), but an exceptionally high dust-to-
gas ratio, possibly associated with the finite lifetimes of the gas
molecules released at the onset of the outburst as compared to long-
lived dust grains.  A significant contribution to relatively high
dust abundance may also be caused by a portion of the dust tail
remaining within the photometer apertures due to projection effects
from the comet's small phase angle.
     Further naked-eye total-magnitude estimates (cf. IAUC 8887):
Oct. 27.63 UT, 2.4 (Y. Nagai, Gunma, Japan); 28.10, 2.5 (J. Rao,
Putnam Valley, NY, U.S.A.); 28.75, 2.5 (H. Dahle, Les Olives,
France); 29.54, 2.3 (S. Yoshida, Ibaraki, Japan); 30.76, 2.4 (T.
Karhula, Vasteras, Sweden); 31.76, 2.5 (K. Cernis, Vilnius,
Lithuania); Nov. 1.79, 2.3 (J. J. Gonzalez, Leon, Spain); 2.96, 2.5
(A. Pereira, Cabo da Roca, Portugal).


COMETS C/2007 L12, C/2007 L13, AND C/2007 M4 (SOHO)
     Further to IAUC 8888, additional Kreutz sungrazing comets have
been found on SOHO website images ("discovery" observations
tabulated below).  C/2007 L12 was extremely faint (mag about 8.5-
9.0).  C/2007 L13 and C/2007 M4 were stellar (mag about 5.5) in C3
images.  C/2007 L13 appeared slightly diffuse with a very faint
tail in C2 images.  C/2007 M4 was slightly diffuse and showed a
short, thin, faint tail in C2 images.

 Comet        2007 UT      R.A.(2000)Decl.   Inst.  F    MPEC
 C/2007 L12   June 14.854   5 25.8  +21 22   C2     RM   2007-T122
 C/2007 L13        15.138   5 26.2  +19 58   C3/2   AK   2007-T122
 C/2007 M4         24.696   6 01.0  +19 16   C3/2   TH   2007-U15

                      (C) Copyright 2007 CBAT
2007 November 2                (8889)            Daniel W. E. Green