A 421 d Activity Cycle in the BeX Recurrent Transient A0538-66 from   MACHO monitoring
  We present a ~ 5-yr optical light curve of the recurrent Be/X-ray transient A0538-66 obtained as a by-product of the MACHO Project. These data reveal both a long-term modulation at P = 420.8 +/- 0.8 d and a short-term modulation at 16.6510 +/- 0.0022 d which, within errors, confirms the previously found orbital period. Furthermore, the orbital activity is only seen at certain phases of the 421 d cycle suggesting that the long-term modulation is related to variations in the Be star envelope. 
C. Alcock, R. A. Allsman, D. R. Alves, T. S. Axelrod, A. C. Becker, D.   P. Bennett, P. A. Charles, K. H. Cook, A. J. Drake,...