Central Bureau for Astronomical Telegrams
IAUC 3325: Cyg X-2; P/SCHWASSMANN-WACHMANN 1
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Read IAUC 3326
Circular No. 3325
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM Telephone 617-864-5758
CYGNUS X-2
S. A. Ilovaisky, C. Chevalier, C. Motch and E. Janot-Pacheco,
Observatoire de Meudon, communicate: "Analysis of x-ray observations
of Cyg X-2 obtained by G. Branduardi, K. O. Mason, N. E.
White and P. W. Sanford with the 2.5-7.5-keV Mullard Space Science
Laboratory detector on board the Copernicus satellite reveals that
between 1973 and 1977 a 9.843-day 35-40-percent relative-flux modulation
appears only during low-intensity states (100-200 counts/min)
in 1974 Sept. to Dec., 1975 Oct. and 1976 Nov. with x-ray minimum
occurring at spectroscopic phase 0.5, hereinafter referred to as x-ray
phase 0.0 (x-ray source behind the optical star; cf. IAUC 3292,
3318). During high-intensity states (200-350 counts/min) in 1975
June and 1976 Oct. no such modulation is detectable. The 1976 Oct.
data show a flux maximum at x-ray phase 0.0, and a narrow and deep
(58-percent relative amplitude) minimum appears at x-ray phase 0.5
(x-ray source in front of optical star). The bottom of this minimum
(residual flux 130 counts/mm) is 14 hr wide, and the transition
from high to low intensity takes place in 6 hr. Rapid dips in
the x-ray flux lasting 20-30 min are observed in the high states at
several phases. The hardest spectra are found during the phase-0.0
1974 minima. The high-state data show an overall softer spectrum
with no apparent correlation between intensity and spectral shape,
especially during the dips. Simultaneous optical photometry obtained
at the Haute Provence Observatory in 1975 Oct. and 1976 Oct.
shows no direct correlation between x-ray and optical fluxes. In
1976 Oct., when the x-ray source was at its highest level at phase
0.0, the optical star was near minimum (B = 15.3). A few days
later, during the x-ray minimum at phase 0.5, the star was brighter
by 0.3 magnitude in B. Optical variability (0.4 magnitude on timescales
of several hours) has been observed at all phases. A strong
U-B vs. B correlation is present at all brightness levels, while
B-V remains constant. Simultaneous photometric and spectroscopic
observations in 1976 Oct. and 1977 Aug. show that the strength of
the He II 4686 A emission line is directly correlated with the U
flux. No C III-N III 4630-4650 A emission is present in our spectra.
Absorption-line radial-velocity measurements confirm the
9.843-day period."
PERIODIC COMET SCHWASSMANN-WACHMANN 1
Total visual magnitude estimate by J. Bortle, Brooks Observatory
(32-cm reflector): Feb. 4.09 UT, 12.7.
1979 February 7 (3325) Brian G. Marsden
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