Ellipsoidal variability of symbiotic giants
  One of fundamental questions in relation to symbiotic binaries is the process of mass transfer - Roche lobe overflow or stellar wind - and possibility of an accretion disc formation. The presence of secondary minima in the quiescent light curves of YY Her, CI Cyg and BF Cyg apparently due to ellipsoidal changes of the red giant provides here important clues. 
J. Mikolajewska, E.A. Kolotilov, S. Yu. Shugarov, A.A. Tatarnikova,   B.F. Yudin