New emission phase of the Be/X-ray binary X Persei/4U0352+30: Nearly simultaneous spectroscopic and near-infrared observations

We present a series of optical spectroscopic and near-infrared photometric observations of the Be star X Persei, from the beginning of the recent emis sion phase. Our data show that after the latest extended low state (ELS), b oth the equivalent width (EW) of the H alpha emission line and the JHK lumi nosities gradually increased. The recent maximum H alpha EW and JHK magnitu des are more than but comparable to the 1986-1989 maxima, which reflects a more extensive and denser envelope in the new emission phase. The IR photometry and the H alpha EW increase coincidently in the early sta ge of the new emission phase. However, the variations in the following year s, especially in 1994 and 1995, are much different from the early trend. An unusual variation that while the H alpha EW in X Per increases considerabl y, the JHK magnitudes decline rapidly is seen in our nearly simultaneous sp ectroscopic and near-infrared observations. An expanding ring model is put forward to interpret the observed unusual va riation between the H alpha EW and near-IR luminosity during the recent emi ssion phase of X Persei. Our results indicate that although both infrared e xcess and H alpha emission line arise from the envelope, their main contrib utors, in some cases, are likely to originate in the different part of the envelope.