The symbiotic variable SY Muscae has been observed with IUE in September 1980 and June 1981 and in the photographic region in May 1981. The entire ultraviolet spectrum brightened between September and June by about a factor of 5. The spectrum shows high excitation including emission from N v and high electron density, about 10^10 cm^-3 as determined from various line ratios in the ultraviolet. The optical spectrum is dominated by permitted lines; even [0 m] is very weak again indicating high density in the ionized region. The increase in ultraviolet continuum and line emission may be due to enhanced mass transfer from the cool star whose period is 623 d and whose maximum was predicted to occur very close to the time of the June 1981 observations. Alternatively the hot star and much of the emitting gas could have been in eclipse in September 1980.
Michalitsianos, A.G., Kafatos, M., Feibelman, W.A., Wallerstein, G. (1982) A Brightening of the Symbiotic Variable SY Muscae, Astronomy and Astrophysics, 109: 136-140.