Non-LTE effects in streams, and mass-transfer rates in three eclipsing binaries

A mass-transferring stream in an eclipsing binary is seen in projection against the hot star in roughly the quarter-period before primary eclipse. At this time a small fraction of the light of the hot star is blocked by the stream, depressing light curves slightly. Five-color observations of such light curves in AQ Cas, RZ Sct, and U Sge are discussed. Non-LTE and LTE predictions of stream-produced light losses with these observations are compared, the validity of this mechanism is discussed, and mass-transfer rates are estimated. 22 refs