[IAUC] IAUC 8753: C/2006 S4; RS Oph [25139-2007/05-R1]

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                                                  Circular No. 8753
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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COMET C/2006 S4 (CHRISTENSEN)
     E. J. Christensen reports the discovery of another comet on
Catalina Sky Survey images obtained with the 0.68-m Schmidt
reflector (discovery observation tabulated below), the object
displaying a 1'.8 fan-shaped tail spanning p.a. approximately
210-250 deg in a stacked image of four 30-s exposures obtained in
poor seeing.  Following posting on the 'NEO Confirmation Page', M.
Tichy and J. Ticha write that their CCD images taken on Sept. 22.99
UT with the 1.06-m KLENOT Telescope at Klet show a diffuse 10" coma
and a tail in p.a. 260 deg.  P. Birtwhistle (Great Shefford,
Berkshire, U.K., 0.40-m f/6 Schmidt-Cassegrain reflector) reports
that his CCD images taken on Sept. 23.1 show a coma of diameter 10"
with central condensation and a tail 40" long in p.a. 245 deg.

     2006 UT             R.A. (2000) Decl.       Mag.
     Sept.22.37326    1 50 43.48   -16 25 58.4   16.8

The available astrometry, the following preliminary parabolic
orbital elements, and an ephemeris appear on MPEC 2006-S53.

     T = 2007 Apr. 26.414 TT          Peri. =  28.144
                                      Node  =  28.811   2000.0
     q = 2.89250 AU                   Incl. =  52.670


RS OPHIUCHI
     M. Orio and T. Nelson, Istituto Nazionale di Astrofisica and
University of Wisconsin, report that RS Oph (cf. IAUC 8671, 8695)
was observed with XMM-Newton on Sept. 6 for about 15 hr.  The count
rate in the range 0.1-10 keV had decreased by more than a factor of
1000 with respect to the last XMM-Newton observation on Apr. 6.
The unabsorbed flux is at least 4 x 10**-12 erg cm**-2 s**-1.
There is still significant continuum flux below 2 keV, but the
spectrum shows mainly strong emission lines.  With the RGS
spectrograph, several H-like and He-like emission lines of Mg, Ne,
and Fe are detected (most notably Ne VII at 2.478 nm, O VIII at
1.896 nm, Ne X at 1.213 nm, and Fe XVII at 1.501 nm).  The RGS
lines are red-shifted with a velocity not exceeding 500 km/s.
Despite the lack of significant flux above 2 keV, two emission
lines of the iron triplet K(alpha) complex are detected with EPIC
around 6.4-6.7 keV.

                      (C) Copyright 2006 CBAT
2006 September 23              (8753)            Daniel W. E. Green