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IAUC 6511: C/1995 O1; GX 5-1

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                                                  Circular No. 6511
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
Phone 617-495-7244/7440/7444 (for emergency use only)

     D. Bockelee-Morvan, Observatoire de Paris; R. Moreno, Institut
de Radio Astronomie Millimetrique (IRAM); N. Biver, P. Colom, J.
Crovisier, E. Gerard, E. Lellouch, and H. Rauer, Observatoire de
Paris; W. Dent and J. K. Davies, Joint Astronomy Centre, Hilo; D.
Despois, Observatoire de Bordeaux; and G. Paubert, IRAM, report
observations of HNC, HCN, CO, CH3OH, and H2S with the IRAM 30-m
telescope and of OH with the Nancay radio telescope on Nov. 8-10:
"The J(1-0) line of HNC at 90.7 GHz was detected with a line area
of 0.040 +/- 0.008 K km sE-1, on the brightness-temperature scale.
For comparison, the HCN J(1-0) line intensity is 0.90 +/- 0.04 K km
sE-1.  The 157-GHz lines of methanol show a rotational temperature
of 45 +/- 2 K.  The following production rates were measured:  CO,
1.3 x 10E29 molecules/s; HCN, 1.1 x 10E27; CH3OH, 2.6 x 10E28; H2S,
1.3 x 10E28; OH, 1.1 x 10E30."

GX 5-1
     M. van der Klis and R. Wijnands, Astronomical Institute 'Anton
Pannekoek', University of Amsterdam; E. Kuulkers, Oxford University;
F. K. Lamb and D. Psaltis, University of Illinois at Urbana; S.
Dieters, University of Alabama at Huntsville (UAH); J. van Paradijs,
UAH and University of Amsterdam; W. H. G. Lewin, Massachusetts
Institute of Technology; and B. Vaughan, California Institute of
Technology, report: "RXTE observations of the low-mass x-ray binary
(and Z source) GX 5-1 made on Nov. 6 and 16 show high-frequency
quasiperiodic oscillations (QPO).  Power-density spectra of the 10-
50-keV flux show two QPO peaks in the range 325-895 Hz.  The
centroid frequency of the stronger of the two peaks increases from
567 +/- 14 to 895 +/- 12 Hz, its width decreases from 230 +/- 40 to
50 +/- 40 Hz, and its rms amplitude decreases from 6.7 +/- 0.5 to
2.0 +/- 0.3 percent (10-50 keV) from the left end of the horizontal
branch to the top of the normal branch in the x-ray color-color
diagram (i.e., for increasing mass-accretion rate).  The weaker of
the two peaks is only detected in part of this range, at a
frequency that increases with accretion rate from 325 +/- 9 to 448
+/- 25 Hz.  The frequency separation of the two peaks is consistent
with being constant near 325 Hz.  The peaks are at least 1.3 to 2.4
times weaker in the band 1-10 keV than in the band 10-50 keV.  GX
5-1 is the second Z source (after Sco X-1; IAUC 6319) to show kHz

                      (C) Copyright 1996 CBAT
1996 November 26               (6511)            Daniel W. E. Green

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