A spectral study of the Be/X-ray binary LSI+61°303

Abstract New optical intermediate dispersion spectra of the periodic radio star LSI +361°303 are presented. The Hα emission line shows a typical hell absorption spectrum, which means that the primary of this Be/X-ray binary may be a nearly equator-on Be star. The Hα emission line profile and its variation are analyzed, and some parameters such as the Hα EW and V/R peak ratio change strongly near the radio maximum, and may exhibit periodic variability. Instead of having a wider minimum lasting for about half an orbital cycle as radio flux and V magnitude do, the Hα EW shows a deep minimum at phase ∼ 0.75. The accretion disk around the neutron star formed near its periastron passage is suggested to be responsible for the change when it eclipses the primary and its envelope.