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IAUC 6685: COMETS C/1997 L3 AND C/1997 L4; C/1995 O1

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                                                  Circular No. 6685
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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COMETS C/1997 L3 AND C/1997 L4
     C. St. Cyr, Naval Research Laboratory, reports, for the SOHO-LASCO
Consortium (which consists of the Naval Research Laboratory, Laboratoire
d'Astronomie Spatiale, Max-Planck-Institut fur Aeronomie, and the University
of Birmingham), the discovery of two more comets in images obtained by
the LASCO white-light coronagraphs C2 and C3 aboard the ESA/NASA
Solar and Heliospheric Observatory (SOHO) spacecraft.  Both comets are
of mag 4-5 and show faint tails.  The first comet, C/1997 L3, was
discovered by Shane Stezelberger, and the second, C/1997 L4, was discovered
by Darren Lewis.  The following approximate discovery positions are
summarized from the more complete reductions by G. V. Williams on MPEC
1997-M07 and 1997-M08 from measurements of apparent solar distance and
position angle by St. Cyr and Lewis:

     1997 UT           R.A. (2000) Decl.
     June 12.523       5 18.7      +19 01       C/1997 L3
     June 14.355       5 28.9      +19 02       C/1997 L4

The comets were observed until June 13.631 and 15.771, respectively.
St. Cyr suggests that both comets are Kreutz sungrazers, although he
notes that there is an 8-deg difference in the position angles of the
comets at comparable elongations from the center of the sun.  Orbital
computations by the undersigned confirm that both comets are indeed
Kreutz sungrazers, but that the two objects, although at perihelion only
two days apart (at June 13.85 and 15.91, respectively), seem to belong
to different subgroups (Marsden 1967, A.J. 72, 1170; 1989, ibid. 98, 2306),
immediately suggesting that the number of small Kreutz members must be
very large indeed and the process of producing new members from those
that survive perihelion passage almost continuous.  It appears that
C/1997 L3 belongs to Subgroup II (which includes C/1882 R1 and C/1965 S1),
while C/1997 L4 belongs to Subgroup I (which includes C/1843 D1 and
C/1963 R1).  Further details are on the MPECs cited above.

     Total visual magnitude estimates: May 26.35 UT, 1.3 (T. Lovejoy,
Brisbane, Queensland, Australia; naked eye); 29.90, 1.6 (R. Lourencon, Jundiai,
Brazil, naked eye); June 2.43, 2.0 (A. Pearce, Subiaco, Western Australia,
naked eye); 7.88, 2.1 (J. G. de S. Aguiar, Campinas, Brazil, 11 x 80
binoculars); 14.44, 2.7 (Pearce, City Beach, Western Australia; 20 x 80
binoculars); 17.44, 2.8 (Pearce).

                      (C) Copyright 1997 CBAT
1997 June 20                   (6685)              Brian G. Marsden

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