On the formation of hydrogen shell spectrum and the envelopes of some shell stars

The formation of shell absorption lines in the Balmer series shell stars is considered. The expression for the line profiles is given, considering a large-scale velocity field due to differential rotation, etc. Without any appreciable Balmer progression, the problem is simplified, and an envelope is specified with the fractional area of stellar disk screened by the envelope, and the mean optical thickness of the envelope in Hα line. Applications were made to six shell stars; the values of β and tau (Hα) were estimated from measurements of the radial velocity and central intensity of shell lines. The envelope is well specified by either a single set of β and tau (Hα) or two sets. The equatorial radii, electron densities and masses of the envelopes of these stars were estimated under the assumption of rotational broadening and equator-on model. The results were also compared with the models of the circumstellar envelopes of Be stars derived from the infrared and polarization data. The agreement is satisfactory. The possible effect of continuous emission from the envelope is considered; no appreciable influence on the present analysis is seen. (Mori, K.)