Spectrographic observations of peculiar stars.

1. The spectra of several absorption O-type stars showing vestiges of Wolf-Rayet emission have been investigated from λ 3300 to λ 6700. The absorption spectrum consists mainly of H, He II, He I,O III,O IV, N III, N IV, and Si IV. The emission lines show a P Cygni character and are confined to H, He I, and a few transitions of He II, N III, N IV, N V, C III, and Si IV. The location of the expanding shell giving rise to the emission and absorption lines is estimated. 2. The visual spectrum of P Cygni reveals strong Fe III lines originating from metastable levels (dilution effect). Lines of other elements show a peculiar selectivity of the emission lines. The spectra of three other P Cygni type stars (Z Canis Majoris, BD+47°3487, and BD+11°4073) are described, especially in connection with the phenomena arising in expanding shells. RY Scuti shows a strong system of forbidden [Fe III] lines, and the variations in the spectrum of this star are discussed. 3. The ultraviolet region of the spectrum of ξ Tauri shows several sets of absorption lines (H, He, and ionized metals) arising from the reversing layer and from various layers in the surrounding shell. The a5D - 4p5P0 multiplet of Fe III was the most conspicuous feature in the visual region of γ Cassiopeiae in March, 1940. New data are given for the spectra of several other stars with extended shells (MtW 143, HD 218393, HD 160529, and HD 190073). A group of stars showing forbidden [Fe II] lines is discussed (WY Geminorum, W Cephei, B 1985, B 5481, and HD 45677) ; and new [Fe II] multiplets are found in the ultraviolet region of these objects. 4. The spectra of four binary systems showing simultaneously an M-type spectrum and forbidden lines of high excitation are described in detail. The spectroscopic phenomena accompanying the recent outburst of Z Andromedae are discussed; the continuous absorption in the shell plays an important role in the relative intensities of the emission and absorption components of the P Cygni type lines. The two stars AX Persei and CI Cygni have very similar bright-line spectra, of which the nebular part shows a very high excitation; besides H, He I, and He II, the strongest lines are due to [Fe VII] and [Ne V], and there is good evidence in favor of [Fe X]. The temperature of the nucleus exciting these nebular lines must be of the order of 150,000°, or more. Another multiple object of lower excitation is R Aquarii, and new spectroscopic data show the occultation effect of the nebula by the TiO atmosphere of the late-type component. There is good reason to beUeve that the binary nature of a star stimulates the process of shell formation