Spectral evolution of HBV 475 (= V1329 Cygni) in the ultraviolet

Extract

Figure 1 shows the low resolution IUE spectra of HBV 475 during 1979-81. Whereas the May 1981 spectrum looks very similar to that of June 1979, there is a clear difference in the August 1980 spectrum when the star was brighter. The strength of the NV multiplet at 1240 A surpasses those of the preceeding and succeeding years by at least a factor 4. A first glance at the continuum and the strongest lines suggests a strong activity increase between June 1979 and August 1980, followed by a decrease to the 1979 level by May 1981. Closer inspection shows that neither CIII]λ1908 nor NIII]λl750 followed that activity pattern, but rather decreased steadly in their fluxes. Thus in June 1979 CIII]λ1908 showed the same flux as HeIIλ1640, whereas in May 1980 CIII] was weaker by a factor two. The 0Iλ1304 and MgIIλ2800 multiplets show the same behaviour as HeII, CIV and NV.