LONG-TERM SPECTROSCOPIC MONITORING OF BA-TYPE SUPERGIANTS .2. HIGH-VELOCITY ABSORPTIONS IN BETA-ORI AND HD-96919

During our extended monitoring campaigns on late B and early A-type su pergiants (Kaufer et al. 1996, Paper I) we have observed extraordinari ly deep and highly blue-shifted absorption events in the H alpha line. In this work, new time-series observations showing the most extreme c ases of such events observed so far are presented for two objects, bet a Ori (B8 Ia) and HD 96919 (B9 Ia). The development of these high-velo city absorption (HVA) events in velocity and time are discussed: the H VAs show no signs of spherically symmetric mass-loss events with subse quent accelerated propagation into the wind. The absence of unshifted line emission in connection with the HVAs is especially indicative of the non-sphericity of the active circumstellar regions. Simultaneously with the blue-shifted absorption, red-shifted absorption is found in Balmer and metallic lines, primarily during the onset of the developin g event, which clearly reveals the complex structure of the involved v elocity fields. Mass outflow and mass infall are present in the envelo pe. As a picture for the circumstellar structures that cause the sudde n appearance of the HVAs over a large velocity range, localized region s of enhanced mass loss on the stellar surface, which build up extende d, rotating streak lines in the equatorial plane are suggested. Finall y, the role of a critical ionization structure in the condensed struct ures is discussed.