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IAUC 6452: 1996 PW; Cyg X-2

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                                                  Circular No. 6452
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
Phone 617-495-7244/7440/7444 (for emergency use only)


1996 PW
     MPEC 1996-P03 contains observations and a preliminary orbit for an
asteroidal object with a record high e.  1996 PW was identified and
recognized as unusual by Gareth Williams, Minor Planet Center,
Harvard-Smithsonian Center for Astrophysics, in two nights
(Aug. 9 and 12) of general asteroidal data from the NEAT
program, carried out under the direction of Eleanor Helin, Jet
Propulsion Laboratory, using images obtained with the GEODSS telescope
at Haleakala.  More recent observations demonstrate that e > 0.99,
with other elements T = 1996 Aug. 8, Peri = 182 deg, Node = 144 deg,
i = 30 deg, q = 2.537 AU, H = 14.0.  Imaging by D. Jewitt on Aug. 16
with the University of Hawaii's 2.2-m reflector showed the object as
a point source, devoid of coma in integrations that would easily show
the coma of (2060) = comet 95P/Chiron, for example.  Photometry by
D. Rabinowitz, Jet Propulsion Laboratory, at the Table Mountain
Observatory on Aug. 14.4 UT yields V = 17.9, V-R = +0.31 +/- 0.05,
V-I = +0.60 +/- 0.05 (assuming solar values V-R = +0.367, V-I = +0.705).


CYGNUS X-2
     A. P. Smale, NASA/Goddard Space Flight Center and Universities Space
Research Association; E. Kuulkers, Astrophysics Division, ESTEC,
European Space Agency; and R. A. D. Wijnands, Astronomical Institute
'Anton Pannekoek', University of Amsterdam, report: "The public RXTE
ASM lightcurve (covering the interval 1996 Feb. 22-Aug. 8) of the
9.8-day low-mass x-ray-binary Cyg X-2 shows a pronounced intensity
modulation with a period of 77.0 +/- 1.0 days and full amplitude of
40 percent.  A shallower (20 percent) secondary minimum is also observed.
The spectral hardness and source intensity are anticorrelated on this
cycle.  We find that this long-term periodicity can be detected
independently in the HEASARC archival datasets from Vela 5B (see also
Smale and Lochner 1992, Ap.J. 395, 582) and the Ariel V ASM.  From
these three datasets we derive a single overall ephemeris from 1969
to 1996 of HJD 2442202.5 (+/- 5.0) + 77.13 (+/- 0.05) E (where phase
zero is the primary minimum).  The occurrence of different intensity
states in the Einstein, EXOSAT and Ginga data from Cyg X-2 (Kuulkers
et al. 1996, A.Ap. 311, 197) is also consistent with this 77.1-day
periodicity, which we tentatively associate with the precession of a
tilted accretion disk in the system."

                      (C) Copyright 1996 CBAT
1996 August 16                 (6452)              Brian G. Marsden

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