We present two-dimensional ( radial velocity , orbital phase ) spectroscopic results for the very low mass-ratio close binary AW UMa which strongly indicate that the spectroscopic mass ratio ( q _ { sp } = 0.10 ) does not agree with the photometrically derived one and that the widely adopted contact binary model appears to experience serious inconsistencies and limitations for this object .
AW UMa is compared with V566 Oph ( q _ { sp } = 0.26 ) which we found to behave according to the contact model .
Observed broadening functions of AW UMa can be interpreted by a very strong limb darkening and/or non-solid body rotation of the dominant primary component ; the former assumption is unphysical while the differential rotation is not supported by an apparent stability of localized , dark features on the outer side of the primary .
There are indications of the existence of an equatorial belt encompassing the whole system .
All deficiencies in the interpretation and the discrepancy between the photometric and spectroscopic mass ratio of AW UMa can be solved within a new model of AW UMa where both components are detached and the system is submerged in a stream of hot , optically thick matter which mimics the stellar contact .
While the masses and their ratio are correctly given by spectroscopy , the photometric picture is heavily modified by the matter engulfing both stars in the equatorial plane .