Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990apj...350..288c&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 350, Feb. 10, 1990, p. 288-294. Research supported by NSF.
Astronomy and Astrophysics
Astronomy
78
Black Holes (Astronomy), Eclipsing Binary Stars, Light Curve, Stellar Spectrophotometry, X Ray Binaries, Emission Spectra, Line Spectra, Spectrum Analysis
Scientific paper
Simultaneous spectroscopic and photometric observations have been made of the optical counterpart of the variable X-ray source CAL 87, an apparent low-mass X-ray binary in the Large Magellanic Cloud. The shape of the optical light curve, showing a deep minimum with very broad wings, suggests an eclipse of a very extended disk structure, which is the dominant light source. The only strong feature in the optical spectrum is a variable He II (4686 A) emission line. Radial velocities of the He II emission lines show a small-amplitude variation (K about 40 km/s) through the orbital period. The phasing of these velocities indicates that the emission arises on the degenerate star side of the center of mass, as is the case for many low-mass X-ray binaries. If this velocity reflects the motion of the compact star, then the mass ratio must be large (about 10), and there is a strong probability that the system may be an eclipsing black hole binary.
Cowley Anne Pyne
Crampton David
Hutchings John B.
Schmidtke Paul C.
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