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IAUC 7267: C/1999 S4; GM Sgr

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                                                  Circular No. 7267
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)
     Another unusual-moving object discovered by LINEAR and
reported as asteroidal, subsequently posted on the NEO Confirmation
Page, has been noted to be cometary in appearance by D. Durig
(Sewanee, TN, 0.3-m f/7 reflector + CCD; coma diameter about 10";
tail about 20"-25" long in p.a. 200-220 deg) and by J. Ticha and M.
Tichy (Klet, 0.57-m f/5.2 reflector + CCD; comet diffuse with 8"
coma and tail > 10" long in p.a. 245 deg).  The discovery
observation is given below, and additional astrometric observations
appear on MPEC 1999-T02:

     1999 UT             R.A. (2000) Decl.        m2
     Sept.27.39772    5 03 47.42   +34 16 45.3   17.3

The following preliminary parabolic orbital elements (from MPEC
1999-T02) suggest that this comet might become a naked-eye object
next July:

     T = 2000 July 18.288 TT          Peri. = 152.651
                                      Node  =  83.387   2000.0
     q = 0.71953 AU                   Incl. = 149.934

1999 TT     R. A. (2000) Decl.   Delta     r    Elong. Phase    m1
Sept.29     5 02.95   +34 24.1   3.851   4.254  107.0   13.0   16.2
Oct.  4     4 59.84   +34 47.4   3.716   4.200  112.4   12.7   16.1
      9     4 55.95   +35 10.8   3.584   4.146  117.9   12.3   15.9
     14     4 51.21   +35 33.9   3.455   4.092  123.5   11.7   15.8
     19     4 45.56   +35 56.1   3.332   4.037  129.2   11.0   15.7


GM SAGITTARII
     P. A. Charles and T. Shahbaz, University of Oxford; and T.
Geballe, Gemini Observatory, report:  "We have obtained a K-band
(1.9-2.5-micron) low-resolution (2.5-nm) spectrum of the x-ray
transient GM Sgr = XTE J1819-254 (IAUC 7253) on Sept. 17.22 UT with
the U.K. Infrared Telescope (+ CGS4).  We estimate K = 12.5 +/-
0.3.  Our spectrum shows a blue continuum and broad emission lines
of He I (2.06 microns; EW = 2.1 nm) and Br-gamma (EW = 1.4 nm),
characteristic of low-mass x-ray binaries.  Both profiles have a
FWZI of about 5900 km/s.  There is clear evidence for an extended
blue wing in the Br-gamma profile, which may be related to a
high-velocity wind component.  Further spectroscopic monitoring
during this outburst is encouraged."

                      (C) Copyright 1999 CBAT
1999 October 1                 (7267)            Daniel W. E. Green

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