[IAUC] CBET 738: 20061113 : COMET C/2006 M4 (SWAN)

[IAUC mailing list]

                                                  Electronic Telegram No. 738
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS en CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT en CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html


COMET C/2006 M4 (SWAN)
     Z. Sekanina, Jet Propulsion Laboratory, California Institute of
Technology, writes that a preliminary inspection of the astrometric
observation of C. E. Woodward et al. from Nov. 7 of a detached-coma feature
(cf. IAUC 8772), suggests that this is a compact cluster of sizable nucleus
fragments, released from the primary at the time of a recent outburst (IAUC
8766).  The cluster, rather than a single fragment, is implied by the
feature's reported elongation along the offset vector, reminiscent of
similar episodes experienced recently by comet 73P's nuclei B, G, and
others.  Assuming, tentatively, 2006 Oct. 23.9 UT for this event's onset
time, the observed offset fits the modeled separation distance perfectly
and leaves a residual of 3 degrees in the position angle, well within
observational errors.  The derived effective differential nongravitational
deceleration, (69 +/- 4) x 10**-5 units of the sun's gravitational
acceleration, implies that the cluster is a short-lived phenomenon,
observable for a few weeks at the most.  The cluster's predicted separation
distances and position angles, relative to the primary nucleus (0h TT,
equinox 2000.0), are:  2006 Nov. 11, 5", 39 deg; Nov. 21, 9", 35 deg; Dec.
1, 13", 31 deg; Dec. 11, 17", 27 degrees.
     Visual total-magnitude and coma-diameter estimates (cf. IAUC 8766):
Oct. 25.72 UT, 4.2, -- (M. Meyer, Frauenstein, Germany, naked eye); 26.77,
4.2, 15' (M. Lehky, Pasinovice, Czech Republic, naked eye); 28.76, 4.5, 10'
(V. Gonano, Udine, Italy, 10x50 binoculars); 30.75, 5.4, 20' (K. Hornoch,
Vohancice, Czech Republic, naked eye); Nov. 1.73, 5.6, 10' (A. Diepvens,
Balen, Belgium, 20x50 binoculars); 6.63, 5.8, 5' (V. Ivanov, Saratov,
Russia, 0.11-m reflector); 8.79, 6.4, 6' (J. J. Gonzalez, Asturias, Spain,
7x50 binoculars); 11.86, 6.5, 9' (J. Carvajal, Madrid, Spain, 6x30
binoculars); 12.78, 6.3, 10' (Gonano).


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2006 CBAT
2006 November 13                 (CBET 738)               Daniel W. E. Green