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IAUC 3802: 1983d

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                                                  Circular No. 3802
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM     Telephone 617-864-5758


COMET IRAS-ARAKI-ALCOCK (1983d)
     The following improved parabolic orbital elements, by the
undersigned, are from observations Apr. 27 to May 9:

                       Epoch 1983 May 10.0 ET
         T = 1983 May 21.1897 ET Peri. = 192.7870
                                 Node  =  48.3992   1950.0
         q =   0.991372 AU       Incl. =  73.3786

A general solution is not viable, although e could be as small as
0.98.  This would affect the current ephemeris (IAUC 3799-3800)
only slightly, the indicated corrections being: May 10.0 ET,
Delta-R.A. = +0m20,  Delta-Decl. = 0'0;  10.5, +0m27, +0'7; 11.0,
+0m16, +2'0; 11.5, +0m09, +2'9;  12.0, +0m05, +2'9;  12.5, +0m04, +2'4;
13.0,  +0m02, +1'6; 14.0, +0m01, +1'0; 15.0, +0m01, +0'6; 16.0, 0m00,
+0'5.

     M. A'Hearn, University of Maryland; and R. Millis, Lowell
Observatory, report that a crude reduction of observations on May
7.4 UT yields OH production (per second) 9 x 10**27 and CN production
5 x 10**25. (The OH lifetime was assumed to be 10**5 s, and the
production goes inversely with lifetime.)  These numbers determine
the radio sensitivity required to search for H2O and HCN.

     From the European Space Angency's Villafranca station M.
Festou, P. Benvenuti, C. Cacciari, A. Cassatella, A. Talavera and
W. Wamsteker report IUE observations on May 6 and 8.  Low-resolution
spectra in the 120-320-nm range showed clear emissions due to
L-alpha, S (weak), CS (very strong), CO2+ doublet (very weak), OH (
moderate): the continuum was very weak.  On May 6 the OH production
rate (per second: vectorial model) was estimated to be 6 x 10**27.
The exceptional CS brightness observed within the 10" x 20" IUE
slit is due to the small geocentric distance and the sharply
peaked CS density distribution.  At closest approach the CS average
brightness might be greater than that of OH.  From the appearance
of the comet spectrum in comparison with earlier IUE observations
it would seem that the comet is not 'new' in the Oort sense.

     Further total naked-eye magnitude estimates: May 7.15 UT, 4.8
(D. W. E. Green, MA); 8.22, 4.4 (Green); 9.38, 3.1 (A. Hale, CA).
Coma diameters in the range 75'-80' (May 8) have been reported.


1983 May 9                     (3802)              Brian G. Marsden

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