Phase changes of the Be/X-ray binary X Persei J. S. Clark, A. E. Tarasov, A. T. Okazaki, P. Roche and V. M. Lyuty A&A, 380 2 (2001) 615-629 Published online: 15 December 2001 DOI: 10.1051/0004-6361:20011468