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IAUC 7256: C/1999 S1; GM Sgr; DD Cir = N Cir 1999

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                                                  Circular No. 7256
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 S1 (SOHO)
    D. A. Biesecker, SM&A Corporation and Goddard Space Flight
Center, reports observations of a presumed Kreutz sungrazing comet
discovered by J. D. Shanklin (Comet Section, British Astronomical
Association) in SOHO/LASCO C3 data (still outside the field of the
C2 instrument).  Astrometry and orbital computations are given on
MPEC 1999-S04.  Biesecker also provides the following apparent
magnitudes (statistical uncertainty +/- 0.1 mag) from a 3x3-pixel
aperture (56"/pixel) centered on the comet's optocenter:  Sept.
17.221 UT, 4.87; 17.263, 4.75; 17.346, 4.54; 17.388, 4.41; 17.431,
4.40; 17.471, 4.42; 17.513, 4.50.

     1999 UT            R.A. (2000) Decl.
     Sept. 16.679     11 07.8       + 1 18


GM SAGITTARII
     B. M. Gaensler, Massachusetts Institute of Technology; D.
Campbell-Wilson and R. W. Hunstead, University of Sydney; and R. J.
Sault, Australia Telescope National Facility, confirm the presence
of transient radio emission from GM Sgr, at a position within 1" of
that previously reported (IAUC 7254).  Observations with the
Australia Telescope Compact Array showed a steady decrease in flux
density from 0.31, 0.31, 0.25, and 0.18 Jy on Sept. 16.16 UT at
1.38, 2.50, 4.80, and 8.64 GHz, respectively, to 0.23, 0.20, 0.13,
and 0.09 Jy on Sept. 16.40.  Observations with the Molonglo
Observatory Synthesis Telescope (MOST) over the period Sept.
16.11-16.32 give a constant 0.843-GHz flux density of 0.28 +/-
0.015 Jy.  The data show an evolution from an optically thick
spectrum to one with a power law having spectral index -0.45.  The
constancy of the MOST flux suggests that the falling opacity and
increasing losses are operating on similar timescales at this
frequency.
     Visual magnitude estimates by B. Monard, Pretoria, S. Africa
(via the AAVSO), and by A. Pearce, Nedlands, W. Australia (P):
Sept. 13.730 UT, 12.3; 14.715, 11.7; 14.749, 11.4; 14.776, 11.1;
14.788, 11.1; 15.700, 10.3; 15.733, 10.5; 15.778, 10.7; 15.825,
11.3; 15.860, 11.4; 15.891, 11.5; 15.927, 11.6; 16.708, 13.7;
17.553, 13.8 (P).


DD CIRCINI = NOVA CIRCINI 1999
     Visual magnitude estimates by H. C. Vital, Rio de Janeiro,
Brazil:  Sept. 3.015 UT, 10.0; 3.904, 10.1; 4.010, 10.2; 4.938,
10.1; 5.958, 10.2.

                      (C) Copyright 1999 CBAT
1999 September 17              (7256)            Daniel W. E. Green

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