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THE ASTRONOMER Electronic Circular No 1549      2000 Aug 06 10.06UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK             GMH at AST.STAR.RL.AC.UK
WORLD WIDE WEB                    http://www.demon.co.uk/astronomer
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COMET C/1999 S4 (LINEAR)
Z. Sekanina, Jet Propulsion Laboratory, reports: "The unusually
large nongravitational forces found by Brian Marsden suggest that
comet C/1999 S4 was a trailing fragment of a more massive comet
that has been moving in the same orbit, arrived at perihelion long
(centuries?) ago but (not surprisingly) was missed.  Trailing
fragments of known comet pairs have a tendency to sudden
disintegration (e.g., Sekanina 1997, A.Ap. 318, L5).
If much of the comet's mass did indeed dissipate into a cloud of
dust in the recent event, as suggested by Mark Kidger (IAUC 7467)
and others, the total mass involved could be estimated by further
monitoring the tail.  Experience with the past initially bright
comets that later became headless and disappeared shows that a
narrow, bandlike tail--a developing synchronic formation--should
survive the head by several weeks or even longer (Sekanina 1984,
Icarus 58, 81).  A very preliminary analysis suggests that
the event may have begun as early as July 23.6 UT and involved
submillimeter-sized and larger dust (repulsive accelerations up to
0.024 of the solar attraction).  The position angle and approximate
length of this tail feature are then predicted to reach:
July 30.0 UT, 90 deg, 2';
Aug. 4.0,     98 deg, 4';
     9.0,    102 deg, 7';
    14.0,    104 deg,10';
    19.0,    105 deg,12';
    24.0,    106 deg,15';
    29.0,    106 deg,17'
IAUC 7471 (extract)

Editor: contrary to messages circulating on the Internet and
appearing in the media, the comet does not appear to have
completely disappeared but has faded considerably.

Brian Manning, Stakenbridge, England reports that he observed the
comet in 20x60 binoculars with m1 estimates as follows:
2000 July 21.01UT, 7.5; 21.99, 6.5
Later estimates by other observers show a clear fade:
2000 July 30.82UT, 8.0 (Tony Tanti, Malta 20x70B)
     Aug   1.85UT, 8.5 (Werner Hasubick, Germany, 25x100B).

The predicted tails mentioned in the above IAUC may prove
difficult to image because of faintness but this unusual
opportunity should be explored and attempts made. Please
e-mail any results to the editor rather than waiting until
the end of the month.

SUPERNOVA 2000da IN UGC 5
A. B. Aazami and W. D. Li, University of California at Berkeley,
 on behalf of LOSS report the discovery with the 0.8-m Katzman
Automatic Imaging Telescope (KAIT) of an apparent supernova on
unfiltered images taken on Aug. 4.5 (mag about 17.8) and 5.4 UT
(mag about 17.5).  The new object is located at R.A. = 0h03m06s.52,
Decl. = -1 54'41".8 (equinox 2000.0), which is 12".8 east and 9".3
north of the nucleus of UGC 5.                       IAUC 7474

SUPERNOVA 2000cz IN IC1535
This object, discovered by Mark Armstrong, has been
spectroscopically confirmed as a type II by S.Jha et.al.IAUC 7474
Guy M Hurst