Be/X-ray binaries are a major subclass of high mass X-ray binaries. There are two Keplerian disks in Be/X-ray binaries, a circumstellar disk around Be stars and an accretion disk around neutron stars.Through the multi-band observations, we could study the formation and the evolution of the two disks. We have established a long-term program to monitor a group of Be stars, especially observable Be/X-ray binaries with the 2.16 m telescope mounted at Xinglong station of National Astronomical Observatories, China (NAOC), since 1992.

We analyze the long-term optical spectroscopic observations on the Be/X-ray binary A0535+26 from 1992 to 2010. Combined with the public V-band photometric data, we find that each giant X-ray outburst occurred in a fading phase of the optical brightness (Figure 1). The anti-correlation between the optical brightness and the Hα intensity during our 2009 observations indicates a mass ejection event had taken place before the 2009 giant X-ray outburst, which might cause the formation of a low-density region in the inner part of the disk. The X-ray outbursts occurred around the periastron point should be connected with the mass ejection from the Be star. The work by Jingzhi Yan, Hui Li and Qingzhong Liu, has been accepted to be published in The Astrophysical Journal of January 2012 (http://iopscience.iop.org/0004-637X/744/1/37).