Electronic Telegram No. 563
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)
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COMET 174P/ECHECLUS
     Y.-J. Choi, P. Weissman, S. Chesley, and J. Bauer, Jet Propulsion
Laboratory; J. Stansberry, University of Arizona; S. Tegler, Northern
Arizona University; W. Romanishin, Oklahoma University; and G.
Consolmagno, Vatican Observatory, report that CCD images of comet 174P
= (60558) taken since 2005 Dec. 30 show that the source of activity
appears to be a secondary body moving independently of the primary.  The
secondary is detected by its bright coma; the nucleus is not resolved.
At the discovery of activity in December, the primary was at V magnitude
20.73, with the secondary coma at V = 16.10 and located about 1".4
northeast of the primary.  The two bodies reached a maximum observed
separation of about 7".0 (the secondary being northwest of the primary)
on 2006 Feb. 25.  On April 20, the primary was at V = 20.35 and the
secondary coma was at V = 16.72.  On May 4, the secondary had moved to
about 2".7 southwest of the primary.  The rapid motion over such large
distance cannot be accounted for by a bound Keplerian orbit unless the
size estimated for (60558) is substantially in error, by a factor of
greater-than or approximately 200 in mass.  The secondary appears to be
moving hyperbolically relative to the primary and may be a fragment
ejected from the primary, or even an escaped satellite since the
secondary appears to be very active but the primary is not at all active.
The secondary body itself may be too small to detect; at that distance,
it could be 5 km in radius and would not be visible because it would be
too faint and obscured by the bright coma.


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2006 CBAT
2006 June 27                     (CBET 563)               Daniel W. E. Green