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IAUC 7455: C/1999 S4

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                                                  Circular No. 7455
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 C/1999 S4 (LINEAR)
     D. Schleicher, Lowell Observatory; and C. Eberhardy,
University of Washington, used the Hall 1.1-m telescope at Lowell
Observatory to obtain narrowband photometry of comet C/1999 S4,
with the following averaged results: June 10-12, log Q(OH) = 28.41,
log Q(CN) = 25.54, log Af(rho) = 2.83 (cf. IAUC 7342); July 13
(seven sets), log Q(OH) = 28.24, log Q(CN) = 25.45; log Af(rho) =
2.55.  The equivalent log Q(water; vectorial) is 28.42 for July 13,
and no significant temporal or aperture variations were observed.
Significant variability was observed during the June observations,
with the gas-production rates on June 11 being 30--50 percent
larger than on June 10, and then on June 12 dropping to 10 percent
less than on June 10.
     Additional visual m_1, coma-diameter, and tail-length
estimates:  July 8.73 UT, 7.3, 8', -- (Y. Nagai, Yamanashi, Japan,
7x35 binoculars); 10.11, 7.5, 5' x 8', 40' (K. Sarneczky, Calar
Alto, Spain, 8x56 binoculars); 11.12, 7.8, 3', 1.2 deg (A. Pereira,
Cabo da Roca, Portugal, 14x100 binoculars); 12.99, 7.0, 6', 0.6 deg
(K. Hornoch, Lelekovice, Czech Republic, 10x80 binoculars); 14.97,
6.8, 3', -- (H. Luethen, Altona, Germany, 10x50 binoculars); 15.34,
7.0, 5'.5, -- (C. E. Spratt, Victoria, BC, 0.08-m refractor; strong
moonlight).
     The following ephemeris, computed from new orbital elements
including nongravitational parameters as published on MPEC 2000-O02,
shows the comet on July 25 to be 0'.7 north of the position given
on IAUC 7449:

2000 TT     R. A. (2000) Decl.   Delta     r    Elong. Phase    m1
July 15     4 41.23   +61 43.9   0.504   0.796   50.3  100.5    6.5
     17     5 49.09   +64 34.6   0.450   0.786   47.5  107.5    6.2
     19     7 24.51   +64 46.9   0.408   0.778   44.2  114.3    6.0
     21     9 02.69   +60 18.3   0.381   0.772   41.2  119.8    5.8
     23    10 14.99   +51 37.3   0.373   0.768   39.8  122.1    5.7
     25    11 00.96   +41 09.3   0.385   0.765   40.6  120.3    5.8
     27    11 30.09   +31 03.0   0.416   0.765   42.9  115.4    5.9
     29    11 49.30   +22 22.2   0.461   0.767   45.6  108.9    6.2
     31    12 02.52   +15 19.3   0.517   0.771   47.9  102.2    6.4
Aug.  2    12 11.96   + 9 42.6   0.580   0.777   49.6   95.7    6.7
      4    12 18.89   + 5 14.7   0.648   0.784   50.6   89.7    7.0
      6    12 24.09   + 1 39.7   0.718   0.794   51.1   84.1    7.3
      8    12 28.08   - 1 15.0   0.790   0.805   51.2   78.9    7.5
     10    12 31.18   - 3 39.1   0.863   0.818   50.9   74.1    7.8
     12    12 33.63   - 5 39.5   0.936   0.833   50.4   69.6    8.1
     14    12 35.58   - 7 21.4   1.009   0.848   49.6   65.5    8.3

                      (C) Copyright 2000 CBAT
2000 July 16                   (7455)            Daniel W. E. Green

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