[IAUC] CBET 2967: 20120106 : COMET C/2011 W3 (LOVEJOY)
quai en eps.harvard.edu
quai en eps.harvard.edu
Jue Ene 5 20:53:18 ART 2012
Electronic Telegram No. 2967
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
CBAT Director: Daniel W. E. Green; Hoffman Lab 209; Harvard University;
20 Oxford St.; Cambridge, MA 02138; U.S.A.
e-mail: cbatiau en eps.harvard.edu (alternate cbat en iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network
COMET C/2011 W3 (LOVEJOY)
Z. Sekanina, Jet Propulsion Laboratory, writes that the persisting
prominent synchronic feature in the tail of this sungrazing comet (cf. IAUCs
9245, 9246) seen in thirteen detailed images, taken between 2011 Dec. 19 and
2012 Jan. 3, is the product of a major outburst (or a series of outbursts)
that peaked during a relatively short period of time centered on Dec. 17.6 +/-
0.4 UT, approximately 1-2 days after perihelion, and probably had begun a
fraction of a day earlier. Two of the images were secured by J. Ebr et al.
on Dec. 19.37 and 20.33 UT with a 0.3-m f/10 Schmidt-Cassegrain reflector, a
robotic remotely-controlled telescope located at the Pierre Auger Observatory
at Malargue, Argentina (as reported by J. Cerny at http://www.kommet.cz); the
remaining eleven images were taken by R. H. McNaught on Dec. 23.75, 24.74,
and daily between Dec. 26.74 and Jan. 3.73 UT with the Uppsala 0.5-m f/3.5
Schmidt telescope at the Siding Spring Observatory (see the following website
URL: http://msowww.anu.edu.au/~rmn/C2011W3.htm).
The predicted orientations of the synchrone, which rotated clockwise
about 18 deg between Dec. 19 and Jan. 3, agree within +/- 1 deg with the
orientations as measured by the author in the available images. The bright
part of the synchrone contains dust particles larger than about 30 microns in
diameter (with radiation pressure acceleration parameter, beta, < 0.04) on
Dec. 19-20, larger than about 40 microns (beta < 0.03) on Dec. 24, larger than
about 80 microns (beta < 0.015) on Dec. 29, and larger than about 120 microns
(beta < 0.01) on Jan. 3 (when the bright part is understood to be the
northern-most 40' of the feature).
In all thirteen images, the synchrone approximately coincides with the
line of symmetry to the much fainter quasi-parabolic envelope of additional
ejecta, consisting of a smaller number of dust particles that -- upon their
ejection (on or before Dec. 17.6) -- acquired lateral velocities mostly
several tens of m/s, with an upper limit of 200 m/s. The sharp spike at the
sunward end of the synchrone, the site of the most massive fragments
(possibly boulder-sized or larger) are located, shows that their separation
velocities were extremely low.
Significantly, in none of the thirteen images is there evidence for a
second tail, consisting of freshly emitted dust and expected in the directions
close to the prolonged radius vector (i.e., to the south of the synchrone and
making with it an angle of 5-6 deg). This finding, as well as the dramatic
change in the comet's appearance between Dec. 19 and 20 and the permanent
loss of the nuclear condensation starting with Dec. 20, suggest that the comet
sustained a severe damage to its nucleus as the source of activity. The
outburst(s) apparently constituted part of the rapidly-progressing process of
cataclysmic fragmentation that was continuing past Dec. 19.4 UT but was
essentially completed by Dec. 20.3. The drop in brightness from Dec. 20 on
is, in this scenario, understood as reflecting basically the rate of dispersal
in space of the dust ejecta released during the Dec. 16-20 period of the
comet's activity.
It appears that, brightness-wise, C/2011 W3 is rivaling the headless
sungrazer C/1887 B1, whose tail was visually detected until about 19 days
after perihelion. However, C/2011 W3 is doing a little better in terms of the
post-perihelion survival of an active nucleus, as comet C/1887 B1 was found
to have lasted for only about 6 hours after its perihelion passage (Sekanina
1984, Icarus 58, 81).
The outburst-related flare-up(s) in the light curve of C/2011 W3 should
show up in the relevant STEREO HI1-A (http://stereo.gsfc.nasa.gov) and SOHO C3
(http://sohowww.nascom.nasa.gov) images -- which, however, are all overexposed
in the critical period of time near perihelion.
Visual total-magnitude, coma-diameter, and tail-length estimates (under
Instrument column, B = binoculars):
2011-2012 UT Mag. Coma Tail length, p.a. Observer Instrument
dia. (degrees)
Dec. 18.33 -1.0 1' Souza 11x80 B
19.32 -0.5 Souza 11x80 B
19.34 0.0 Aguiar 11x80 B
20.34 1.1 Goiato 20x100 B
21.30 2.3 10' > 5, p.a. 235 Souza 11x80 B
21.34 2.1 Aguiar 11x80 B
22.30 3.0 10' 10, p.a. 235 Souza 11x80 B
22.30 2.8 10' 13, p.a. 235 Amorim 10x50 B
22.32 2.6 Aguiar 11x80 B
22.32 2.8 6' 20, p.a. 240 Goiato naked eye
23.31 4.0 6' 15, p.a. 260 Goiato naked eye
23.32 3.2 Aguiar 11x80 B
24.32 3.8 10' 20, p.a. 260 Goiato 7x50 B
27.31 4.9 Aguiar 11x80 B
28.30 5.2 Aguiar 11x80 B
28.30 4.9 15' > 30, p.a. 225 Souza 7x50 B
29.30 5.6 Aguiar 11x80 B
30.31 5.8 Aguiar 11x80 B
Jan. 2.27 6.5 12' 10, p.a. 225 Goiato 7x50 B
2.29 6.3 Aguiar 11x80 B
3.28 6.6 Aguiar 11x80 B
4.31 8.1 5' Goiato 20x100 B
Observers:
W. Souza, Sao Paulo, Brazil
J. G. de S. Aguiar, Campinas, Brazil
M. Goiato, Aracatuba, Brazil
A. Amorim, Florianopolis, Brazil
NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
superseded by text appearing later in the printed IAU Circulars.
(C) Copyright 2012 CBAT
2012 January 6 (CBET 2967) Daniel W. E. Green
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