Central Bureau for Astronomical Telegrams
IAUC 8326: C/2004 F4
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Circular No. 8326
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 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 ISSN 0081-0304
Phone 617-495-7440/7244/7444 (for emergency use only)
COMET C/2004 F4 (BRADFIELD)
Z. Sekanina, Jet Propulsion Laboratory, writes: "The comet's
peculiar shape in the SOHO's C3 coronagraphic images is caused by
two effects. The gradual coma broadening in a direction nearly
perpendicular to the apparent motion, beginning before Apr. 18.8
UT, is caused by a rapid development of the comet's post-perihelion
dust tail, which points to the southwest from the nucleus in the
images taken around Apr. 19.5 and to the west in the more recent C3
images. The increasingly rugged boundary of the tail on its
antisolar side, especially well pronounced after Apr. 18.8, is due
to discrete features protruding through the tail's smooth leading
edge. These protrusions are either streamers -- i.e., synchronic
formations that are products of recurring events of briefly
elevated dust emission (outbursts) -- or striae (i.e.,
pseudosynchronic formations of a more complex nature). If they are
streamers (perhaps a more likely case, judging from their
appearance in the images just before the comet's head left the C3
field-of-view), their sequence suggests fairly consistently an
outburst recurrence period of about 0.5 day, which might indicate
the comet's rotation period. For example, in the image of Apr.
19.496, one can identify at least seven features, whose position
angles are estimated at between 150 deg and 240 deg, with the
corresponding calculated event times between 2.4 days before
perihelion and 0.6 day after perihelion. The peak radiation-
pressure accelerations on the particles in the features are
estimated at about 2-3 times the sun's gravitational acceleration."
K. Battams, Naval Research Laboratory, has reported
measurements of the position of C/2004 F4 from the SOHO C3 images.
The reduced astrometry by B. G. Marsden and R. Kisala and the
following orbital elements appear on MPEC 2004-H37.
T = 2004 Apr. 17.129 TT Peri. = 333.298
Node = 222.992 2000.0
q = 0.16749 AU Incl. = 63.118
2004 TT R. A. (2000) Decl. Delta r Elong. Phase Mag
Apr. 20 1 24.29 +14 20.3 0.837 0.205 7.4 140.9 2.5
25 1 03.97 +25 36.5 0.938 0.345 20.1 91.1 4.4
30 0 59.13 +32 24.5 1.067 0.491 27.2 69.6 5.8
May 5 1 00.16 +37 00.6 1.190 0.627 31.8 58.0 6.9
10 1 03.54 +40 28.2 1.302 0.754 35.3 50.7 7.7
15 1 07.85 +43 15.8 1.405 0.874 38.2 45.7 8.3
(C) Copyright 2004 CBAT
2004 April 20 (8326) Daniel W. E. Green
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