Circumbinary Components of Contact Binaries
  The period changes of contact binaries obtained by the analysis of eclipse minima timing are found mostly chaotic in nature. However, they are representable by a few cyclic changes superposed on a secular change. The cyclic changes are caused most probably by the third components revolving around the contact binaries. Some typical examples of the period changes of contact binaries are presented in the present contribution. 
O. Demircan, \.I Bulut
astro-ph.SR