A radio outburst and jet from the symbiotic star CH Cyg

Abstract

CH Cyg is an M7 III star that is known to undergo periods of brightening in the blue-violet continuum at irregular intervals of a few years1–3. During the active phase, the spectrum also exhibits strong Balmer emission and emission lines from He I, Fe II and various forbidden transitions, giving it the appearance of a symbiotic star. As part of a monitoring programme on symbiotic stars, observations with the National Radio Astronomy Observatory Very Large Array (VLA) have been made on CH Cyg over the past year at intervals of a few months. During the period April 1984 to May 1985 this monitoring revealed a strong radio outburst coincident with the production of a multi-component jet, and a comparison of high-resolution maps at two epochs separated by 75 days shows that the jet is expanding at a rate of 1.1 arc s yr−1. The onset of the radio outburst coincides in time with a remarkable decline in the visual brightness of the star. The luminosity of the star during the optically active state and the energetics of the mass loss suggest that the outburst is the result of accretion at, or near, the Eddington limit onto the surface of a white dwarf.