Wei Liu

Hello, I am Wei Liu. My research interest is Be/X-ray binaries. A Be/X-ray binary is a system which contains a Be star and a compact star. Be stars' luminosity class is III--V, and at some point of their lives they have shown spectral lines in emission. Be stars have circumstellar disks on their equator planes. When the compact stars pass through the periastrons, they can accrete materials from circumstellar disks. The materials fall into the gravitational potential well, at the same time, their gravitational energy turns into the internal energy, and emit outward in X-ray. In optical and infrared bands, Be stars have two main observational characteristics, spectral emission lines and an excess of IR emission. Both emission line and IR excess originate from the circumstellar disk of the Be star. The optical emission variation of Be/X-ray binaries is dominated by Be star's disk. My aim is to study the multiwavelength long-term variability of Be/X-ray binaries before and after giant X-ray outbursts. Until now, RX J0440.9+4431, Swift J0243.6+6124, 1A 0535+262, and KS 1947+300 were studied in details. We have obtained optical spectroscopy and photometry data before, during, and after the X-ray outbursts. The long-term photometric light curve and the equivalent widths of the Halpha and He I lambda6678 lines were used to monitor the state of the Be star's circumstellar disk. The Halpha line profiles qualitatively show evidence for V/R variability that was accounted for by fitting the Halpha spectral line profile with two Gaussian functions.We divided our data into different phases according to the intensity of the X-ray, optical, and infrared emission to more specifically study changes in the sources.