New emission phase of the Be/X-ray binary X Persei: nearly simultaneous spectroscopic and near-infrared observations

Abstract

We present a series of optical spectroscopic and near-infrared photometric observations of the Be star X Persei, from the beginning of the recent emission phase. Our data show that after the latest extended low state (ELS), both the equivalent width (EW) of the Hαemission line and the JHK luminosities gradually increased. The recent maximum HαEW and JHK magnitudes 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 HαEW increase coincidently in the early stage of the new emission phase. However, the variations in the following years, specially in 1994 and 1995, are much different from the early variations. An unusual variation that while the HαEW in X Per increases considerably, the JHK magnitudes decline rapidly is seen in our nearly simultaneous pectroscopic and near-infrared observations. An expanding ring model is put forward to interpret the observed unusual variations between the HαEW and near-IR luminosity during the recent emission phase of X Persei. Our results indicate that although both infrared excess and Hαemission line arise from the envelope, their main ontributors, in some cases, are likely to originate in the different part of the envelope.