Central Bureau for Astronomical Telegrams
IAUC 3234: V861 Sco = OAO 1653-40
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Read IAUC 3235
Circular No. 3234
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
V861 SCORPII = OAO 1653-40
R. S. Polidan, Princeton University Observatory; P. W. Sanford,
N. E. White and G. S. G. Pollard, University College, London; and
M. C. Locke, Appleton Laboratory, write: "Observations with the
Copernicus satellite of the eclipsing binary star V861 Sco (HD
152667) have led to the discovery of an eclipsing x-ray source (OAO
1653-40) with a period consistent with that of the binary star
(7.848 d). Two x-ray eclipses have been observed at ingress. The
duration of the eclipse is at least 1.75 d. The observed x-ray
flux is approximately 10 Copernicus counts (the Crab Nebula yields
375 counts). There is no evidence for any modulation greater than
15 percent peak to mean flux in the range 3 to 40 min. The
identification of the x-ray source with V861 Sco suggests a compact
object in the binary system. X-ray eclipses occur when the B0Ia
primary star occults the unseen companion. The beginning of the x-ray
eclipse is coincident with the time of occultation of the secondary
object by the primary star within the uncertainties of the extrapolated
ephemeris of the binary star. The mass function derived from
analysis of the orbit of the primary star (Walker 1971, Monthly
Notices Roy. Astron. Soc. 152, 333) is 0.487 Msol. The range of
possible masses for the B0Ia primary star suggests a secondary mass of
between 5 and 12 Msol. Ultraviolet observations obtained in three
spectral regions (1110-ll30, 1167-1185 and 1230-1247 A) during the
x-ray eclipse indicate a stellar spectrum similar to that of kappa Ori.
Broad, strong, violet-displaced (by about -700 to -800 km/s) absorption
components are seen in C III 1176 A and N V 1238 A and
1242 A. Weak N V emission may also be present."
G. J. Peters and J. Dobias, University of California at Los
Angeles and University of Southern California, have obtained H-alpha
observations of V861 Sco with the Lick Observatory's coude auxiliary
telescope and the cooled 40-mm Varo image tube. Three plates were
taken (dispersion 16 A/mm) during June 11-14 at phases 0.047, 0.626
and 0.799 (zero phase being defined as the beginning of the x-ray
eclipse; ephemeris from Polidan et al.). H-alpha is in emission (I/Ic ~
1.5) with a weak central reversal. At phases 0.626 and 0.799, V/R
~ 0.9 and 0.7, respectively. However, at phase 0.047, just after x-ray
eclipse, the V lobe of H-alpha is substantially depressed (V/R ~
0.2), indicating that most of the H-alpha emission emanates from the
accretion disk about the x-ray star.
1978 June 27 (3234) Brian G. Marsden
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