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IAUC 6975: 52P; XTE J2123-058; N Sgr 1998; C/1998 M6

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IAUC number

                                                 Circular No. 6975
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
URL http://cfa-www.harvard.edu/iau/cbat.html
Phone 617-495-7244/7440/7444 (for emergency use only)

     A. Maury, Observatoire de la Cote d'Azur, found this comet to
be undergoing what is apparently a significant outburst near m_1 =
12.2 (m_2 = 14.47) on CCD images on July 21.1 UT (predicted
magnitude about 21; cf. MPC 31833).  The outburst has been
confirmed by other CCD astrometrists (M. Tichy and Z. Moravec at
Klet; H. Mikuz and J. Skvarc at Crni Vrh; and R. Greimel and D. D.
Balam at Victoria) and by visual observers.  Available total-
magnitude and coma-diameter estimates (visual unless otherwise
noted):  July 22.01, 10.9, 2'.8 (K. Hornoch, Lelekovice, Czech
Republic, 0.35-m reflector; comet diffuse); 22.03, 12.3, - (Tichy
and Moravec, 0.57-m f/5.2 reflector + CCD; m_2 = 14.2); 22.04,
11.8, 1'.2 (R. J. Bouma, Groningen, The Netherlands, 0.25-m
reflector; low altitude); 22.07, 12.9, 1'.0 assumed (Mikuz and
Skvarc, 0.36-m f/6.7 reflector + V filter + CCD; tail about 2' long
in p.a. 258 deg); 22.47, 11.0, - (Greimel and Balam, 1.82-m
reflector + CCD).

XTE J2123-058
     S. A. Ilovaisky and C. Chevalier, Observatoire de Haute-
Provence (OHP), write:  "CCD photometry of the optical counterpart
of this x-ray transient (IAUC 6957) has been obtained at OHP with
the 1.2-m telescope during July 3-18 UT.  Our V-band data yield a
unique period of 5.9567 +/- 0.0033 hr, identical to that reported
by Tomsick et al. (IAUC 6972).  In addition to this modulation, we
find that the mean brightness changes from night to night.
Analysis of the differences between the individual curves and the
average template shows that the mean brightness is modulated by
0.3-mag (peak-to-peak) with a 7.2-day (+/- 0.1) period, which could
be related to disk precession.  The V light curve, when corrected
for these baseline changes, has a full amplitude of 0.8 mag and
exhibits pronounced variability near maximum light; it is
remarkably similar to the published light curve of 4U 2129+47 in
its active state, including a 'shoulder' in the descending branch
at phase 0.85."

     Visual magnitude estimates by K. Hornoch, Lelekovice, Czech
Republic:  July 2.93 UT, 11.4; 19.896, 11.5; 20.886, 11.6; 21.874,

Corrigendum.  This comet's name was given incorrectly on IAUC 6974.

                      (C) Copyright 1998 CBAT
1998 July 22                   (6975)            Daniel W. E. Green

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