A phase change in X Persei

We present a series of optical spectroscopic and infrared photometric observations of the Be/X-ray binary system X Per made over the last four years. Over this period the H α line profile changed from emission to absorption, accompanied by a decrease in the infrared flux by over a magnitude and a flattening of the infrared spectrum. Such behaviour is consistent with the loss of the circumstellar disc or shell of material around the Be star and the reversion to a ‘normal’ O/B-type star. Whilst such behaviour has been seen in the optical spectra of many other Be/B stars before, this is only the second time such observations have been made for a star in a high-mass X-ray binary system. Furthermore, the contemporaneous optical and infrared data provide some of the first direct evidence that the near-infrared excess and Balmer line emission do indeed arise in the same circumstellar material.