A systematic study of variability among OB-stars based on HIPPARCOS photometry L. Lefèvre, S. V. Marchenko, A. F. J. Moffat and A. Acker A&A, 507 2 (2009) 1141-1201 Published online: 03 September 2009 DOI: 10.1051/0004-6361/200912304