Long-term optical spectral observations of the Be/X-ray binary LSI+61 degrees 303: evidence of H alpha emission associated with the neutron star

We present the optical spectra of the periodic radio star LSI +61 degrees 3 03 with intermediate dispersion. The H alpha emission line profile and its variation an analyzed. Variability in LSI +61 degrees 303 is observed on di fferent timescales. During our observations the equivalent width (EW) of H alpha line showed long-term variability that is likely to be associated wit h the 4-year period. We suggest that the long-term variability is connected to the intrinsic behaviour of the Be star. The H alpha EW changed strongly around the radio maximum, clearly displayed a maximum at phases between 0.55-0.6, and possibly both another maximum at phases around 1.0 and a minimum between radio phases 0.7-0.9. The only thr ee spectra that showed nearly equal intensities of the two peaks of H alpha emission line all occurred at radio phases around 0.8. It is interesting t o note that the H alpha emission line in 1995 October showed unusual variat ion at radio phases around 0.6, where the decrease of the H alpha emission accompanied by the enhancement of the emission at the red wing. These short -ten and periodic phenomena can be fairly explained with the X-ray induced H alpha emission by employing the orbital solution deduced from near-infrar ed Light curves (Marti & Pandes 1995). Thus provides some evidence for a co rrelation with the orbital motion of the neutron star.