¹STScI/ CSC, Space Telescope Science Institute, 3700 San Martin Dr. Baltimore, MD 21218; email:  msmith@stsci.edu
² Catholic University of America
³ Astronomy Centre, CPES, Sussex University, Falmer, Brighton, BN1 9QJ, UK

We present phase-resolved spectra of the Be/X-ray pulsar system X Persei/4U0352+309 obtained with the Tübingen far-UV echelle spectrometer of ORFEUS/SPAS-2. Data were obtained in November 1996 and folded on the  837.5 sec pulsar period derived from contemporaneous X-ray observations. Contrary to optical results by several groups, we find no evidence for periodic modulation in our FUV line profile data. The limits we can place on the presence of any periodic signal are  1% of the continuum level in the Si IV 1394 line and  1.6% in N V 1238. We have also combined these ORFEUS spectra with newly reprocessed IUE data to discover radial velocity variations in X Per which are consistent with a period of the order of 20-30 years and a binary separation of  20 AU. Even with a wide separation for this system, we argue that certain types of reported rapid variability as well as long-term X-ray enhancements could be caused by the residue of expanding Be discs falling onto the neutron star. The UV resonance lines appear to be typical for a classical Be star, showing variability on timescales of a day and also a few hours.

1999, ApJ, 522, 444