Spectral transformation of the unusual variable star MWC560 to resemble a nova

Abstract

MWC560 is an emission-line star catalogued¹in 1943 and later described² as an 'extraordinary symbiotic-like variable'. It was recently found³ to be undergoing a photometric and spectroscopic outburst. A dramatic change has occurred in the ultraviolet spec-trum of MWC560, so that it now closely resembles the spectrum of a nova shortly after outburst. This event, detected by the International Ultraviolet Explorer satellite, may signal a major mass-ejection episode such as presumably occurred in past centuries in the symbiotic star R Aquarii to produce the well-known bipolar nebula, and it may herald the emergence of a standard symbiotic-star emission-line spectrum in MWC560, corresponding to a change in evolutionary state.