2001A&A...368..471H

We model FeII 5317 emission lines and phase resolved HeI 6678 and 5876 emission lines of the bright B2e&sdO shell binary φ Per to find the size and shape of the excitation region inside the circumprimary disk. We find the FeII 5317 emission to originate within 9 stellar radii in an axisymmetric disk around the primary. Orbital phase variations of HeI 6678 are fit in terms of a disk sector with disk radius of 10 stellar radii and opening angle of ≃120° facing the secondary. This region can be alternatively described by an intersection of a sphere around the secondary and the circumprimary disk with a penetration depth of about 7R_*. Similar fit values are found for HeI 5876. The enigmatic orbital phase precedence of shell occurrence in the HeI emission features is discussed. We favor a model in which the inner HeI shell is deformed because of differential rotation in combination with a finite recombination time.