Central Bureau for Astronomical Telegrams
IAUC 4101: AC 211; GX 349+2
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Circular No. 4101
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 617-495-7244/7440/7444
AC 211
M. Auriere, European Southern Observatory, Garching, and Pic
du Midi Observatory; J. P. Cordoni, Laboratoire d'Astronomie,
Montpellier; and L. Koch-Miramond, C.E.N. Saclay, communicate: "We
obtained esposures of AC 211, the possible optical counterpart for
the M15 globular cluster x-ray source (Auriere et al. 1984, A.Ap.
138, 415), on the three consecutive nights July 21-23, in good to
excellent seeing, using UBV filters with the CCD at the f/25
Cassegrain focus of the 2-m Pic du Midi telescope. The star was
generally in a bright state (e.g., the averaged observed magnitude and
colors between July 22.00 and 22.08 UT were U = 14.6, U-B = -1.2,
B-V = -0.1, all +/- 0.2). We observed a sudden decrease in U on
July 22, the star fading to U = 14.6 during the hour preceding
July 22.12. These observations confirm that AC 211 has photometric
properties that do not fit those of normal globular cluster
stars but are consistent with those of some low-mass x-ray binaries.
The data obtained up to now suggest a binary composed of a
neutron star and a post-main-sequence companion, and possibly an
eclipsing system. Because AC 211 is included in the 98-percent-
confidence error circle of the Einstein Observatory's HRI observations
(Grindlay et al. 1984, Ap.J. 282, L13) it can be considered
as the optical counterpart of the M15 x-ray source."
GX 349+2
W. H. G. Lewin, Massachusetts Institute of Technology; J. van
Paradijs, University of Amsterdam; F. Jansen, Space Research
Laboratory, Leiden; M. van der Klis, European Space Agency; and M.
Sztajno and J. E. Trumper, Max-Planck Insitut fur Extraterrestrische
Physik, telex: "We have detected low-frequency noise (LFN),
below ~ 4 Hz, and may have discovered quasiperiodic oscillations
(QPO) in the average power spectrum of the fluctuations in the x-
ray flux of the bright bulge source GX 349+2 = 4U 1702-36. The
observations were made using EXOSAT during 1984 Sept. 11.81-12.04
UT. The significance of the peak in the power spectrum is only
3.0V. The centroid frequency and FWHM of the peak are ~ 11 and ~
7.5 Hz, respectively. The integrated excess power in the peak and
the LFN (integrated down to 0.5 Hz) correspond to rms variations
of the signal of 2 and 6 percent, respectively. This may be the
fifth bright x-ray bulge source to show the LFN/QPO phenomenon."
1985 September 6 (4101) Brian G. Marsden
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