FeII line widths as tracers for the geometry of Be star envelopes

Extract

The geometry of Be star envelopes is not directly observable, apart from those very few cases where interferometry has been successful. This is even more true for the kinematical conditions in these envelopes. An indirect measure of kinematics, density law and geometry can be achieved by comparing line widths of photospheric absorption lines (⇔ v_* sin i) and circumstellar emission lines (⇔ v(r) sin i). Hitherto existing determinations of line widths have been, however, quite unsatisfactory. The reason is that in these studies Balmer line parameters were used [see Hanuschik (1989) and references therein] which are strongly broadened by radiative transfer and Thomson scattering in addition to kinematic broadening. Because the question of geometry and kinematics is of crucial importance for understanding the Be phenomenon, I have started a new study, using measurements of the Fe ii λ5317 line. This line shows almost optically thin emission and is broadened primarily by kinematics.