2015A&A...581A..37L

Mass loss is an important property in evolution models of massive stars. As up to 90% of the massive stars have a visual or spectroscopic companion and many of them exhibit mass exchange, mass-loss rates can be acquired through studying the period of massive binaries. Using our own photometric observations as well as archival data, we searched for variations in orbital periods of seven massive eclipsing binary systems in the Cygnus OB2 association and estimated their mass-loss rates and stellar parameters. We used a Bayesian parameter estimation method to simultaneously fit the period and period change to all available data and a stellar modelling tool to model the binary parameters from photometric and radial-velocity data. Four out of the seven selected binaries show non-zero period change values at two-sigma confidence level. We also report the eclipsing nature of the star MT059 for the first time.