Electronic Telegram No. 473
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
     Further to IAUC 8693, the astrometry for six new fragments of comet
73P were published on MPEC 2006-G10, having the following times of
perihelion:  component 'U', 2006 June 9.02 TT; 'V', 9.08; 'W', 8.51;
'X', 8.58; 'Y', 8.81.
     Component 'G' appears to be in outburst, as reported by several
observers.  E. J. Christensen reports that unfiltered 120-s CCD images
taken by R. E. Hill with the Mt. Lemmon 1.5-m Schmidt telescope on Apr.
7 UT show 'G' to be considerably brighter than on Apr. 2, with a 1'.5
coma and a 2' tail in p.a. 230 deg.  E. Guido and G. Sostero report a
3-mag increase in the brightness of component 'G' between Apr. 2.36 and
7.31 from unfiltered CCD images taken with a 0.25-m reflector remotely
near Mayhill, NM.
     Sostero adds that, on images obtained on Apr. 8.32 and 9.03 with a
Cousins R filter, component 'B' shows an elongated coma without a clear
central condensation, spanning almost 8" toward p.a. 220 degrees.  The
integrated magnitudes of the inner coma appear now to be decreasing,
after a peak reached on Apr. 6.30; Guido and Sostero supply the following
R magnitudes in a 0'.4 photometric aperture:  Apr. 5.31, 10.5; 6.30,
10.3; 6.99, 10.4; 8.32, 10.7; 9.02, 10.8; 10.32, 11.1.  The Af(rho) value
on Apr. 10.32 was measured as 230 cm -- an almost-threefold decrease
compared to the Af(rho) peak of component 'B' on Apr. 6.30.  They remark
that the aspect of the coma is reminiscent of the coma of C/1999 S4
during the initial phases of its disruption.  Additional imaging of
fragment 'B' on April 11.88 by M. and V. Gonano (0.25-m reflector + CCD +
Cousins R filter at Remanzacco, Italy) shows that the extremely elongated
coma is strikingly similar to the "lance shape" of C/1999 S4 in the
advanced phases of its break-up; no clear photometric center could be
found -- the brightest pixel was placed approximately in the middle of
the 12" elliptical coma, which itself showed an extremely flat
photometric profile.
     C. W. Hergenrother reports that a co-added 630-s Sloan i-band
image of component 'B' obtained with the Mt. Hopkins 1.2-m reflector on
Apr. 11.38 UT showed no sharp central condensation but rather a diffuse
'bar' about 8" in length, extended in the anti-solar direction.  A
co-added 630-s image from Apr. 9.43 showed a more condensed central
condensation, though not as condensed as that of component 'C' on the
same night.  He noted no secondary nuclei around component 'B'.
Christensen adds that Mt. Lemmon images on Apr. 7 showed component 'B'
to have a coma diameter approximately 12' x 15', elongated toward p.a.
230 deg, with a faint narrow tail extending at least 30' toward p.a.
230 deg.
     Christensen further reports that Hill's images on Apr. 7.3-7.5 UT
showed that fragments of 73P were extended roughly 12 degrees in length
on the sky.  Component 'R' is continuing to brighten with a 40" coma
and a 1'.5 tail in p.a. 230 deg.  Components 'K' and 'S' appear as two
2 overlapping fragments of low surface brightness.


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

                         (C) Copyright 2006 CBAT
2006 April 12                    (CBET 473)               Daniel W. E. Green