LONG-TERM SPECTROSCOPIC MONITORING OF BA-TYPE SUPERGIANTS .1. H-ALPHA, LINE-PROFILE VARIABILITY

We have obtained time series of spectra in the wavelength range 4000 - 6800 Angstrom over several months with high S/N and high resolution i n wavelength (lambda/Delta lambda approximate to 20000) and time (Delt a t approximate to 1 d) of the late-type B and early-type A supergiant s HD 91619 (B7 Ia), beta Ori (B8 Ia), HD 96919 (B9 Ia), HD 92207 (A0 I a), HD 100262 (A2 Ia) and alpha Cyg (A2 Ia). H-alpha is found to show broad emission extended to about +/- 200 km s(-1) for all objects exce pt alpha Cyg. Due to the lack of strong line emission in H-alpha the e lectron-scattered photons are expected to originate in deep atmospheri c layers. In all of the objects the H-alpha-line profiles are found to be highly variable on different time scales reaching from days to mon ths. Patterns of variation in H-alpha are found to be quite symmetric about the systemic velocity and are mainly due to variable blue and re d-shifted emission superimposed on almost constant photospheric and/or wind profiles. These V/R variations are interpreted in terms of axial symmetry of the envelopes of these objects. Time-series analyses of t he variations reveal H-alpha time scales up to a factor of 6 longer th an expected radial fundamental pulsation periods but consistent with r otational periods. Therefore, rotational modulation as a possible sour ce of variability is concluded. Corotating weak magnetic surface struc tures are suggested as the source for a rotationally modulated lower w ind region. Suddenly appearing deep and highly blue-shifted absorption s in H-alpha are ascribed to instabilities of the ionization structure of the wind. Outwards propagating discrete absorption components have been observed only once in HD 92207.