Electronic Telegram No. 464
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html


COMET 73P/SCHWASSMANN-WACHMANN
     Component 'B' has gone into outburst, as indicated by the
following total visual magnitude estimates (cf. IAUC 8685):
Mar. 20.89 UT, 12.0 (K. Hornoch, Lelekovice, Czech Republic,
35-cm reflector); 28.07, 12.1 (J. J. Gonzalez, Leon, Spain,
20-cm reflector); 31.67, 11.9 (S. Yoshida, Ibaraki, Japan, 40-cm
reflector); Apr. 2.02, 11.7 (M. Reszelski, Szamotuly-Galowo, Poland,
41-cm reflector); 2.85, 10.7 (Reszelski); 2.86, 11.1 (Hornoch);
3.15, 10.8 (J. Bortle, Stormville, NY, 41-cm reflector); 3.16, 10.8
(Gonzalez; coma diameter 3'); 4.15, 10.6 (A. Amorim, Florianopolis,
Brazil, 18-cm reflector).  Bortle notes that component 'B' appeared
on Apr. 3.15 as a bright, sharp, star-like object with a very faint,
surrounding 'haze'.  G. Sostero and E. Guido, Remanzacco, Italy,
report the following unfiltered CCD magnitudes and photometric
apertures for component 'B', obtained remotely with a 0.25-m
reflector near Mayhill, NM:  Mar. 26.43, 12.7, +0'.6; Apr. 2.36,
11.3, +2'.7; 4.01, 9.6, +2'.7; 5.31, 9.1, +3'.2.  They add that the
computed Af(rho) parameter (cf. IAUC 7342) showed a threefold increase
(from nearly 48 cm to nearly 150 cm) between Mar. 29.4 and Apr. 2.4.
F. Manzini, Sozzago, Italy, reports that his CCD observations show an
increase in brightness of component 'B' of at least 3 magnitudes
between Apr. 1.8 and 2.8; he adds that two bright jets in p.a. 90 deg
during Apr. 2.90-3.05 and 3.85-4.11 and in p.a. 305 during Apr.
3.85-4.11 seem to be related to the ourburst.

     Selected visual total-magnitude and coma-diameter estimates of
component 'C' (considered the primary component of 73P):  Mar. 24.94 UT,
10.8, 2'.0 (A. Baransky, Pylypovychi, Ukraine, 0.36-m reflector); 28.15,
10.2, 3'.0 (J. J. Gonzalez, Leon, Spain, 25x100 binoculars; 0.3-deg tail
in p.a. 255 deg); 29.25, 10.2, 2' (W. Robledo, Pozo del Tigre, Argentina,
0.20-m reflector); 31.66, 9.6, 3'.0 (S. Yoshida, Ibaraki, Japan, 0.40-m
reflector; 6' tail in p.a. 255 deg); Apr. 2.01, 9.8, 2'.5 (M. Reszelski,
Szamotuly-Galowo, Poland, 41.0-cm reflector); 2.84, 10.2, 2'.4 (K.
Hornoch, Lelekovice, Czech Republic, 0.35-m reflector); 3.14, 10.0, 1'.5
(J. Bortle, Stormville, NY, 41-cm reflector); 4.15, 10.3, 1' (A. Amorim,
Florianopolis, Brazil, 0.18-m reflector).

     Sostero and Guido report that their ten co-added 60-s unfiltered
CCD images taken on Mar. 26.43 UT show a companion to component 'G',
located almost 6" in p.a. 260 from 'G' and showing a small coma of
diameter almost 9" and total mag 18.2 (limiting mag close to 19).  K.
Sarneczky, University of Szeged, reports that component 'G' had a
"dumbbell"-shaped coma on Mar. 20.1, with a separation between its two
optocenters of 2".5 along p.a. 80-260 deg; by Apr. 1.1, the coma of 'G'
appeared as a 12"-long bar, the distance between the two optocenters
then being 6".7 aligned in p.a. 73-253 deg.  S. Garro, Var, France,
reports that his CCD images taken with a 27.9-cm Schmidt-Cassegrain
reflector show that component 'G' appeared as a 6"-long elongated
nuclear condensation on Mar. 22-23, but that images taken on Apr. 1-2
and 2-3 show two components clearly separated by 8" in the direction of
the tail.  L. Buzzi, Varese, Italy, reports that CCD images taken with a
0.60-m reflector shows that the new companion to component 'G' was of
mag about 18, < 10" from 'G' in p.a. 240 deg, and more diffuse than 'G',
but moving parallel to 'G', on Apr. 2.16.  E. J. Christensen, Lunar and
Planetary Laboratory, reports that images obtained with the Mt. Lemmon
1.5-m reflector on Mar. 25 show the inner coma of component 'G' to be
elongated, measuring approximately 2" x 5", with the long axis oriented
along p.a. 260.  Christensen's 120-s images on Apr. 2.4 in good seeing
clearly show a second condensation within the tail of component 'G',
located approximately 8" toward p.a. 255 from 'G'; it is difficult to
tell the true extent of the condensation due to its location within the
tail, but its appearance is more diffuse than the primary.
     Z. Sekanina, Jet Propulsion Laboratory, points out that recent
reports of a duplicity of fragment 'G' confirm advancing fragmentation
of the comet.  Based on the Apr. 2 astrometry by E. J. Christensen, the
results from an approximate, two-parameter fragmentation model suggest
that the observed subnuclei of 'G' separated from their common parent
around Mar. 6, with an estimated uncertainty of a few days, and that the
companion has had a relatively high nongravitational deceleration,
typical for short-lived fragments.  The model gives a separation of 2".8
at p.a. 253 deg on Mar. 25, in good agreement with Christensen's
description of the fragment's elongated inner coma.  The companion's
predicted separation from the main fragment and the position angle are
as follows (0h TT):  Apr. 5, 10", 247 deg; 10, 17", 244 deg; 15, 29",
242 deg; 20, 48", 240 deg.


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

                         (C) Copyright 2006 CBAT
2006 April 5                     (CBET 464)               Daniel W. E. Green