¹ Astronomical Institute, Academy of Sciences of the Czech Republic, CZ-25165 Ondrejov
² Institut für Astronomie und Astrophysik und Universitäts-Sternwarte München, Scheinerstr. 1, D-81679 München, Germany
³ European Southern Observatory, Karl-Schwarzschildstr. 2, D-85745 Garching, Germany
⁴ Landessternwarte Königstuhl, 69117 Heidelberg, Germany

We present new phase resolved observations of emission lines of the Be binary  Per. Analyzing the orbital phase variations in the HeI emission features we find strong arguments that the feature as a whole originates in the outer parts of the disk around the primary star. In addition to the HeI 6678 and 5876 lines, the emission features with orbital phase variations were detected in three more HeI lines. The observations are in agreement with the scenario of Poeckert and others, in which the outer parts of an axisymmetric disk are illuminated by the radiation of the secondary. The observations after 1996 are consistent with a growing global density inhomogeneity in the circumprimary disk as it occurs in disks of single Be stars. The combination of the illumination effect and the increasing density inhomogeneity make  Per an ideal laboratory to study density perturbations of circumstellar disks of Be stars in more detail.

Astronomy and Astrophysics 358, 208-220 (2000)