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IAUC 7123: C/1999 C1; XTE J1550-564; C/1998 P1

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                                                  Circular No. 7123
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  ISSN 0081-0304
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COMET C/1999 C1 (SOHO)
     D. A. Biesecker, NASA Goddard Space Flight Center, reports
observations of a probable Kreutz sungrazing comet in SOHO/LASCO C3
and C2 data on Feb. 6 and 7.  The comet was a relatively bright one,
with a tail over 0.25 deg long, and it was discovered by D. Lewis,
University of Birmingham, in C3 data at a projected heliocentric
distance of about 25 solar radii.  The last observation was in C2
data some 28 hr later at about 3.9 solar radii.

     1999 UT             R.A. (2000) Decl.
     Feb.  6.459       21 49.2       -17 59

Astrometric measurements, made by Biesecker and S. Gregory and
reduced by G. V. Williams, are given on MPEC 1999-E18, together
with orbital elements by B. G. Marsden.

XTE J1550-564
     R. Remillard, E. Morgan, and A. Levine, Massachusetts
Institute of Technology; J. McClintock and G. Sobczak, Center for
Astrophysics; C. Bailyn and R. Jain, Yale University; and J. Orosz,
Pennsylvania State University, write: "There is continued evolution
of the high-frequency quasiperiodic oscillations (QPO) in the x-ray
nova and blackhole candidate XTE J1550-564 (see IAUC 7121).  An
RXTE PCA observation on Mar. 5.52 UT reveals a QPO at 283 +/- 5 Hz
with a FWHM of 39 +/- 9 Hz, and an rms amplitude of 4.0 +/- 0.7
percent at 6-30 keV, similar to that reported for Mar. 4.80.
However, subsequent PCA observations show changes as follows:  235
+/- 6 Hz (FWHM 30 +/- 11; amplitude 2.8 +/- 0.8 percent at 6-30 keV)
on Mar. 7.50; 182.0 +/- 2.5 Hz (FWHM 12 +/- 4; amplitude 0.91 +/-
0.23 percent at 2-30 keV) on Mar. 8.37.  Thus the frequency has
returned to the value at which the QPO was originally discovered
(IAUC 7025).  The steep increase in amplitude with photon energy
(IAUC 7121) has lessened on Mar. 8, as the QPO is weakly visible in
the band 2-6 keV, while the profile fits have poor quality when the
energy range is restricted to 6-30 keV."

     Visual m_1 estimates:  Feb. 6.61 UT, 9.2 (S. Yoshida, Ibaraki,
Japan, 0.25-m reflector); 18.95, 9.5 (J. Carvajal, Madrid, Spain,
0.21-m reflector); 25.15, 10.7 (R. J. Bouma, Groningen, The
Netherlands, 0.25-m reflector); Mar. 6.78, 10.9 (K. Hornoch,
Lelekovice, Czech Republic, 0.35-m reflector); 8.82, 10.9 (M.
Meyer, Frauenstein, Germany, 0.25-m reflector).

                      (C) Copyright 1999 CBAT
1999 March 9                   (7123)            Daniel W. E. Green

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