Radio Stars and X-ray Sources

Abstract

SEVERAL weak, highly variable radio sources have been shown by excellent optical-radio positional agreement (∼ 1 arc s) to be associated with optically bright binary stars^1–13. One of these radio stars, associated with the optical binary HDE-226868 (refs 10–16) has been suggested as the optical-radio counterpart of the strong variable X-ray source, Cyg X-1 (a frequently discussed candidate for a black hole). We report limits on the X-ray emission from the known radio stars that can be studied with Uhuru. These results are of interest because of the possible association between X-ray binaries and radio star binaries, and because limits or measurements of the X-ray fluxes can help determine the source of the radio emission. A strong limit (comparable to those reported here) on the X-ray emission from the optical-binary β Persei during periods of radio flaring has recently been reported by the MIT OSO-7 group¹⁷.