OGLE-III counterpart to SMC X-2 reveals 18.62 day binary period

The OGLE-III optical data of the two possible counterparts to SMC X-2 (SXP2.37) have been extensively analysed. The first 5 years of OGLE-III data for both these stars is presented in Schmidtke el al 2006 (AJ, 132,971). They find no significant periodicities in either star and propose the brighter more northern star to be the true counterpart due to the large variations in its light curve. Two further years of OGLE-III data for both stars are now available making a total of 7 years coverage.