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IAUC 7403: P/2000 ET90

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                                                  Circular No. 7403
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)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7244/7440/7444 (for emergency use only)


COMET P/2000 ET90 (KOWAL-MRKOS)
     MPS 11479 contains observations on Mar. 9 and 13 by LINEAR of an
apparently asteroidal object presumed to have a moderately eccentric orbit
in the inner part of the main belt.  Linkage by G. V. Williams to LINEAR
observations on Apr. 4 and 8 demonstrated the cometary nature of the orbit,
and the object was placed in The NEO Confirmation Page.  Isolated observations
from LINEAR on Feb. 7, from the Catalina Sky Survey on Mar. 1 (when observer
T. B. Spahr had in fact drawn attention to the object's "slowish" motion) and
from LONEOS on Apr. 2 were then also linked.  Neither these observers nor
those responding to the Confirmation Page made a definite remark about the
object's cometary appearance, even in response to specific enquiries from
the Central Bureau (although strong moonlight has recently been a factor).
Following a suspicion by the undersigned and an independent suggestion by
C. W. Hergenrother, 2000 ET90 has been definitively identified with comet
D/1984 H1 = 1984 JD (Kowal-Mrkos) = 1984n (IAUC 3988, 4001) = 1984 X, for
which current predictions (ICQ Comet Handbook for 2000, p. H87; OAA Comet
Handbook for 2000, p. 37) require correction by Delta T about -125 days.
The comet passed only 0.16 AU from Jupiter in Mar. 1989.  The rediscovery
position and orbital elements (from 47 observations 1984-2000, mean residual
0.7 arcsec) follow.  There was an unobserved return with T = 1991 Aug. 2.
The hitherto unpublished astrometry, residuals and an ephemeris are given
on MPEC 2000-G52.

     2000 UT             R.A. (2000) Decl.        m2
     Mar.  9.30345   11 38 37.03   - 5 21 29.0   18.9

                    Epoch = 1984 May  20.0 TT
     T = 1984 June  8.3272 TT         Peri. = 338.3150
     e = 0.484237                     Node  = 249.3254  2000.0
     q = 1.949042 AU                  Incl. =   2.9538
       a =  3.778947 AU    n = 0.1341677    P =   7.346 years

                    Epoch = 2000 June 25.0 TT
     T = 2000 July  1.8035 TT         Peri. = 320.5886
     e = 0.409022                     Node  = 245.5014  2000.0
     q = 2.546791 AU                  Incl. =   4.6837
       a =  4.309452 AU    n = 0.1101720    P =   8.946 years

                      (C) Copyright 2000 CBAT
2000 April 15                  (7403)              Brian G. Marsden

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