Abstract
Aims. The main goal of this study is to investigate the relationship between the optical and X-ray behaviours of the Be/X-ray binary system SAX J2103.5+4545.
Methods. We present the relations between the H alpha equivalent width, optical brightness and X-ray flux of the system, by analysing the optical photometric and spectroscopic observations together with the X-ray observations.
Results. The X-ray outburst of the system occurred just after the optical outburst. The nearly symmetric H alpha emission line profiles observed during the beginning of the optical outburst turn into asymmetric profiles with increased EW values during the dissipation of the Be disc. A correlation between the H alpha emission line strength and the X-ray flux was found. The H alpha line indicates the existence of an equatorial disc around the Be star. The H alpha line changed from emission to absorption during the observation period. The observed double peaked HeI emission lines might come from the accretion disc of neutron star which is temporarily formed at the time of X-ray outburst.