Spectroscopic Observations of 48 Librae.

Abstract

Radial velocity-Between 1904 and 1931, spectrograms at various observatories indicated a nearly constant velocity; but between 1935 and 1944 a fluctuation of considerable amplitude occurred. At the extreme velocities a progression in displacement from line to line along the Balmer series was observed. Microphotometer tracings showed the bright Ha line to be more nearly stationary than its dark core. Velocities from metallic lines agree with those of H lines near the head of the series. Lines of Na i and Ca II have stationary components which are possibly partly circumstellar. Intensilies of lines-The dark lines of H and of metals-notably lines of Pen, Cr Ii, Ni I', and Ca ii -became stronger from 1938 to 1943. In certain typical lines the equivalent widths more than doubled. The absorption in H 15 increased from 38 to 87 per cent. In the dark core of Ha the absorption became more than 90 per cent, showing that absorbing atoms lay in front of most of the emitting atoms. In 1943 the dark Balmer lines were measured to H 41. The H cores and the metallic lines are narrow but at times asymmetrical. The change in structure does not explain the measured displacements. Discussion-Displacements of the lines are probably due to motions in the stellar atmosphere. The amplitude of the fluctuations seems to increase from the photosphere outward. Several facts suggest that the bright H lines may come from a layer of hydrogen just above the photosphere. This hypothesis may be applicable to other Be stars with shell spectra