Central Bureau for Astronomical Telegrams

IAUC 6906: C/1998 J1

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                                                  Circular No. 6906
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
Phone 617-495-7244/7440/7444 (for emergency use only)


COMET C/1998 J1 (SOHO)
     More than 100 positions were reported (cf. IAUC 6894, MPEC 1998-J13,
-J14 and -J21) of this comet as it moved across the top of the field of the
SOHO-LASCO C3 coronagraph between May 3.78 and 8.87 UT.  Attempts to
record the comet from the ground were often inconclusive, mainly because
of the difficulty of predicting the comet's position from the rough SOHO
data.  Visual observations that appear to be positive are: May 11.23 UT,
m1 approx. 0.5, coma diameter D = 0'.5 (N. Biver, Kahe Point, Oahu, HI,
0.26-m reflector); 11.23, m1 approx. 0.5, D = 1'.0 (H. Dahle, same location,
20 x 80 binoculars); 14.35, m1 approx. 2-3, tail about 15' long toward the
east (P. Nation, Christies Beach, South Australia, 11 x 80 binoculars);
16.24, m1 = 3.5, D = 1' and rather condensed with faint, short, fanshaped tail
about 5' long in p.a. 110 deg (Biver); 16.34, m1 approx. 2.5-3, tail >
0.5 deg long in p.a. 90-130 deg (C. E. Drescher, Warrill View, Queensland,
Australia, 7 x 50 binoculars).  In addition, the comet was apparently
imaged (focal length 500 mm, ST-6) by O. Farago (Stuttgart, Germany) on May
10.8 UT, when the close proximity to the Pleiades allowed J. Jahn
(Bodenteich, Germany) to perform astrometry (internal consistency about 2")
from four stars bright enough for detection in strong twilight at 4.5 deg
altitude in the 1-deg field!  Positions and a compromise parabolic
orbit and ephemeris follow:

        1998 UT             R.A. (2000) Decl.      Observer
        May  10.80208    3 45 03.6    +23 43 15    Farago
             16.249      4 47.7       +12 53       Biver
             16.34       4 48         +12 50       Drescher

     T = 1998 May   8.352 TT          Peri. = 107.649
                                      Node  = 355.021   2000.0
     q = 0.15015 AU                   Incl. =  68.346

1998 TT     R. A. (2000) Decl.     Delta      r    Elong. Phase      m1
May  13     4 13.70    +19 54.2    0.894    0.246   13.1  111.6      1.7
     15     4 35.43    +15 41.6    0.865    0.309   16.7  109.5      2.6
     17     4 54.17    +11 18.8    0.851    0.371   20.8  104.8      3.3
     19     5 10.73    + 7 00.0    0.848    0.432   24.9   99.3      4.0
     21     5 25.62    + 2 52.4    0.853    0.490   28.9   93.8      4.6
     23     5 39.18    - 1 00.0    0.865    0.547   32.7   88.6      5.1
     25     5 51.67    - 4 35.6    0.883    0.603   36.3   83.7      5.5
     27     6 03.27    - 7 54.1    0.905    0.656   39.5   79.2      6.0

                      (C) Copyright 1998 CBAT
1998 May 16                    (6906)              Brian G. Marsden

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