Central Bureau for Astronomical Telegrams
IAUC 4263: AC 211; 1982i
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Circular No. 4263
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
T. Naylor and P. A. Charles, Oxford University; and P. J.
Callanan and R. M. Redfern, University College, Galway, report: "We
have discovered a 9-hr spectroscopic period for AC 211, the optical
counterpart of the M15 x-ray source (cf. Charles et al. 1986,
Nature 323, 417), from observations made using the Isaac Newton
Telescope at La Palma (resolution 0.15 nm on Aug. 1 and 0.08 nm on
Aug. 2-3). Strong, occasionally double-peaked, and broad (2.0-nm)
He II (468.6 nm) emission was present together with He I (404.6,
447.1, and 471.3 nm) absorption. The position of the 447.1-nm line
was fitted with a sine curve to yield a period of 9.1 +/- 0.4 hr, an
amplitude of 45 +/- 15 km/s, and a remarkable gamma velocity of -145
+/- 30 km/s with respect to the cluster. This result suggests that
AC 211 is a low-mass x-ray binary being ejected from the core,
although the exact nature of the secondary is still unclear."
S. A. Ilovaisky and C. Chevalier, Observatoire de Haute-
Provence; M. Auriere and P. Angebault, European Southern Observatory;
L. Koch-Miramond, Saclay; and J. P. Cordoni, Montpellier, telex:
"Analysis of 246 U-band CCD images of the M15 core, obtained
under excellent seeing conditions (0".8 FWHM) with the 3.6-m Canada-
France-Hawaii Telescope at Mauna Kea and the 2-m Pic-du-Midi
telescope in 1985 July, 1985 Sept., and 1986 July, reveals that the
light from AC 211 is modulated by up to 1.7 mag with a probable
period of 8.538 +/- 0.001 hr (several aliases, including one at 8.529
hr, cannot be excluded). There are large changes in the shape and
amplitude of the lightcurve on timescales as short as one orbital
cycle."
PERIODIC COMET HALLEY (1982i)
M. J. S. Belton, Kitt Peak National Observatory, communicates:
"Analysis of 70 pre-perihelion (r > 5 AU) observations using a 3-
component harmonic model for the lightcurve variation, with the
constraint from Vega experimenters that the rotation period is
between 50 and 56 hr, yields fits for either of two periods: 53.96
and 54.12 (+/- 0.03) hr. Direct rotation gives the best result. The
first harmonic (P = 26.985 hr) has the dominant component and a
peak-to-peak amplitude of about 1.1 mag. Observers are encouraged to
obtain photometric series in 1987 Mar. and following, to increase
the accuracy and check the validity of the period."
1986 October 23 (4263) Daniel W. E. Green
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