The interacting binary SCO X-1

Spectroscopic observations of Sco X-1 show conclusively that the emission lines vary in radial velocity with a period of .787 sup d + or - .006 and a full range of approximately 120 km/s. The period is identical to that found by Gottleib et al (1975) from photometric data; light minimum occurs when the emission line region is at superior conjunction. The observations indicate that the emission lines originate in an accretion disk surrounding a neutron star which is orbiting about a normal, although somewhat evolved companion. The light variation is due to a heating effect on the non degenerate star, viewed at a small inclination angle.