The Spectrum of BD+11°4673 during the Years 1937-1941.

This article is the fourth in a series giving detailed data concerning numerous lines in the complex spectrum of the peculiar emission-line star BD+11°4673. A résumé of changes since 1915 is included. The bright lines of H have been wider and more intense than formerly. The 800-day cycle in the dis- placements has continued with little change of phase, but the amplitude has diminished, and the mean velocity has become algebraically smaller. The amplitude apparently had reached a maximum in 1928. L The chief lines of He i have remained prominent. Singlets and triplets behave differently. The negative displacements of the dark components are now greater than at any other time. A feature of special inter- est is the increasing intensity of the bright line X 4686 He ii. Other lines studied include those of Fe ii, [Fe rn], N u, N iii, Si i, Si ri Si m, Si iv, Mg i, and a few of unidentified origin. The dark bands of TiD have gradually grown stronger, until in 1940 and 1941 their intensities were approximately equal to those in class Ml. Thus BD+11°4673 enters the group of stars with combination spectra and may assist in the interpretation of these anomalous objects. An inlercomparison of lines shows many differences in behavior, summarized in Tables 10 and 11. Progressive changes since 1915, illustrated in Figures 1, 6, and 7 (see Tables 2, 4, 6, and 7), include strengthening and widening of bright lines of H and He i; increasing negative displacements of dark lines; a general increase in the ionization of the atmosphere, evidenced by the behavior of lines of He, Fe, N, and Si. The hypothesis of an expanding atnwsphere is briefly discussed. Certain facts suggest that the veloci- ties of atoms increase as they travel outward and that the degree of ionization also increases