1999A&A...345..137P

New and published UBV photoelectric and spectroscopic observations of AW UMa are analyzed and interpreted by a triple or quadruple-star model. The derived inclination angle i=78.3°, the photometric mass ratio q=0.08 as well as all available radial velocities, corrected for the systemic velocity changes, were used to determine the masses of the components of the contact binary as M₁=(1.79±0.14)M_☉ and M₂=(0.143±0.011)M_☉. These values set the binary on the ZAMS. Variations in the systemic velocity suggest the existence of a third body on a P₃=398days orbit with eccentricity e₃=0.227±0.056. Assuming that the orbits of the contact binary and of the third body are coplanar, its mass is M₃=(0.85±0.13)M_☉. The long-term orbital period decrease is explained by mass transfer from the more massive to the less massive component accompanied by the angular momentum loss due to mass outflow from the outer Lagrangian point L₂. The period decrease occurred either suddenly (in two period jumps 6200 days apart) or continuously. In the second case, the (O-C) residuals from the parabolic fit can be explained by the light-time effect caused by a fourth body on a P₄=6250days eccentric orbit (e₄=0.63±0.24). For the most probable range of inclination of the possible fourth component orbit 60°>i₄>40°, the range of its mass is 0.168M_☉<M₄<0.229M_☉.