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The optical behaviour of the Be star in the high-mass X-ray transientA0535+26/HDE245770 shows that at periastron the luminosity is typicallyenhanced by 0.02 to a few tenths magnitude, and the X-ray outburst occurs eightdays after the periastron. Indeed, at the periastron an increase of the massflux occurs. This sort of flush reaches the external part of the temporaryaccretion disk around the neutron star and moves to the hot central parts ofthe accretion disk and the neutron star surface. The time necessary for thisway is dependent on the turbulent viscosity in the accretion disk, as discussedby Giovannelli, Bisnovatyi-Kogan, and Klepnev (2013) (GBK13). In this paper wewill show the behaviour of this system in optical band around the predictedperiastron passage on 21st February 2014, by using the GBK13 ephemeris that weused to schedule our spectroscopic and photometric optical observations.Spectroscopic unusual activity detected in the Balmer lines and the enhancementin the emission in B, V, and R bands around the periastron passage, and thesubsequent X-ray event definitively demonstrate the existence of about 8 daydelay between optical and X-ray flares.

Optical and X-ray behaviour of the high mass X-ray transient A0535+26/HDE245770 in February-March 2014