The Spectrum of BF Cygni.

The variabifity of BF Cyg, discovered by C. R. d'Esterre, has recently been studied by Luigi Jacchia, who found a semiregular period of 754 days. Bright lines in the spectrum were discovered at Mount Wilson in 1925. A detailed study of line intensities and displacements is based on spectrograms taken in 1940, 1941, 1942, and 1943. The star has a "combination" spectrum whose peculiarities differ in degree, rather than in kind, from those of Z And, AX Per, CI Cyg, and AG Peg. The intensities and displacements of numerous bright lines vary in a complex way. The chief lines studied are those of H, He I, Fe ii, [Fe u], [Fe ml, [Ne iii], and [0 rn]. The El lines are very intense with a slow decrement. The lines of [Fe ni} are stronger than in any other stellar spectrum yet observed. The nebular lines [0 rn] and [Ne iu~ are subject to surprisingly rapid variations in intensity, marked changes sometimes occurring within 24 hours. Many details con- cerning the behavior of these and other bright lines are recorded. Certain changes may possibly have some connection with the 754-day period of light-variation. An absorption spectrum, type about gM4, appeared on a few plates. A comparative study of several objects is probably the best approach to the obscure problems of "combination" spectra