The circumstellar shell of Alpha Orionis from a study of the Fe II emission lines.

Nine spectrograms exposed for the A region in a Orionis at 3.4 and 6.7 A have been obtained to study the Fe ii emission lines. Information on the radial velocities, line widths, intensities, and shapes of the 17 Fe ii emission lines from multiplets 1, 6, and 7 comprise the basic data. The Fe II lines appear to follow the motions of the photosphere but are redshifred by an average of 5 km -1 The line widths vary from about 20 to about 80 km 1 from the weakest (relative intensity = 1) to the strongest line (relative intensity = 5.5). The stronger emission lines show self-reversed absorption centers. All the lines are asymmetric in that the shortward side is more intense. A model of a spherical envelope moving with a uniform velocity, which gives an effective velocity gradient of geometrical origin, has been derived to explain the observed features. It is found that the Fe ii lines arise in regions of infalling material with a radius of 2.5 R* and a Doppler broadening of 14 km . This model accounts fairly well for the observed redshifts, asymmetries, widths, intensities, and shapes of most of the lines. The velocity field of the model appears to be too crude to explain all the phenomena, but the random motions which give rise to the broad lines are intimately associated with the mean motion of the infalling material. This can perhaps be explained by motions of large-scale bubbles or convective cells. Subject headings: circumstellar shells - emission-line stars - luminous stars - stars, individual