Photospheric and stellar wind variability in ϵOri (B0 Ia) *

We provide direct observational evidence for a link between photospheric activity and perturbations in the dense inner-most stellar wind regions of the B supergiant star ϵOri. The results, which are relevant to our understanding of the origin of wind structure, are based on a multi-spectral line analysis of optical time-series data secured in 1998 using the HEROS spectrograph on the ESO Dutch 0.9-m telescope in La Silla. A period of ~1.9 days is consistently identified in Balmer, He iabsorption, and weak metal lines such as Si iiiand C ii. The primary characteristic is a large-amplitude swaying of the central absorption trough of the line, with differential velocities in lines formed at varying depths in the atmosphere. The variance resulting from the “S-wave” velocity behaviour of the lines is constrained within ±the projected rotation velocity (~80 km s-1) in the weakest absorption lines, but extends blue-ward to over -200 km s-1in Hα. A second (superimposed) 1.9 day signal is present at more extended blue-ward velocities (to ~-300 km s-1) in lines containing stronger circumstellar components. Inspection of archival optical data from 1996 provides evidence that this modulation signal has persisted for at least 2.5 years. Non-radial pulsational modelling is carried out in an attempt to reproduce the key observational characteristics of the line profile variability. Only limited success is obtained with prograde ($m=-1$) modes. The principal S-wave pattern cannot be matched by these models and remains enigmatic.