Period variations of Algol-type eclipsing binaries AD And, TW Cas and IV Cas

We present new analysis of O-C diagrams variations of three Algol-type eclipsing binary stars AD And, TW Cas and IV Cas. We have used all published minima times (including visual and photographic) as well as new determined ones from our and SuperWasp observations. We determined orbital parameters of the 3rd bodies in the systems with statistically significant errors, using our code based on genetic algorithms and Markov Chain Monte Carlo simulation. We confirmed multiple nature of AD And and triple-star model of TW Cas and we proposed quadruple-star model of IV Cas.