Simultaneous observations of variable stars. I. The Be star pi Aqr.

Results of five days of simultaneous spectroscopic, polarimetric, and photometric observations of rapid atmospheric variations are reported for the Be star pi Aqr. The observational and data processing methods are described, and the variability, rotation, and general spectral features of the star are analyzed. No strongly significant variations on time scales of minutes to days are found in the degree of polarization, the equivalent widths of Balmer lines, or other spectral features. The rotational velocity of the photosphere is derived from the widths of several shell absorption lines and indicates a radial expansion decreasing toward the outer part of the shell. It is concluded that pi Aqr was in a relatively stable and quiet phase during the observations and that slow variations may be occurring in the shell.-