Discovery of a subarcsecond radio binary associated with the SVS 13 star in the HH 7-11 region

We report the discovery of a double radio continuum source (VLA 4A and 4B) associated with the optically visible star SVS 13. The two components of the radio source are separated by 0".3, corresponding to a projected separation of 65 AU for a distance of 220 pc. We propose that the radio sources trace the components of a binary system. The observed separation implies a lower limit of similar to 135 yr for the orbital period, for a binary system with a total mass of 2 M-.. We suggest that, as in other pre-main-sequence binaries, the two components of the system could be in different evolutionary stages and/or suffer from different extinction, with the more extincted object being associated with the previously reported millimeter source, while the other component would correspond to the visible star SVS 13. Since an increase in the optical/near-infrared brightness of the SVS 13 star was observed around 1990, we speculate that such flux variations could be due to the reappearance of the optical component previously occulted by the circumstellar envelope/disk of dust associated with the millimeter component. The observed separation implies a radius of similar to 60 AU for the presumed dust envelope and suggests an orbital period of similar to 1700 yr and a duration of the occultation of similar to 185 yr. We expect that other subarcsecond binary systems, which remain unresolved, could present an anomalous behavior that may be explained by assuming the presence of a binary system whose components are in different evolutionary stages and/or suffer from different extinction.