Spectral features of the B2e star EW Lac before and during the variable shell phase.

Abstract

An examination of the spectral characteristics of the B2e shell star EW Lac before and during the variable shell phase is presented based on 93 spectrograms obtained between 1960 and 1984 with the Haute Provence Observatory coude spectrograph. Characteristics of the prevariable shell phase include radial velocity fluctuations of shell lines of weak semiamplitude without any periodicity, and a flickering of metallic shell line intensity. Characteristics of the variable shell phase include a phase lag between the radial velocity curves of the high Balmer shell lines and that of the deepest part of the H-beta shell core, and an asymmetry of the high Balmer line profiles which is related to their radial velocity. The present results are consistent with the two-zone model of a cool equatorial disk and an expanding atmosphere seen at high latitude.