The Evolution of a Peculiar Stellar Spectrum: Z Andromedae.

The spectral lines of Z Andromedae have been measured on plates taken between May 12 and August 25, 1940, when the brightness had decreased to magnitude 9.7 after the outburst in 1939. The spectrum shows emission lines of a thin and dilute nebula and resembles the spectrum observed by H. H. Plaskett in 1923-1926. There is some evidence of a late-type companion, in addition to a hot nucleus, which re- sembles some of the slow novae, and a fairly pronounced P Cygni type spectrum of an expanding shell. The latter is a remnant of the shell which was formed in the outburst of 1939. The nebular spectrum shows strong forbidden lines, but there are relatively few stages of ionization, which shows that the nebula consists of a fairly thin layer. The intensity of the auroral transition of [0 m}, X 4363, is relatively strong-a phenomenon which is characteristic of other binaries of similar type, and of novae. Among the nebulae the stellar planetary IC ~ shows the same feature. A list of lines of this object is given in Table ~. I. INTRODUCTIO