U Gem - Rediscussion of Radial Velocities and System Parameters

Radial velocities measured from peaks of the emission lines (Smak 1976, Stover 1981), analyzed within the three-body approximation, give K1 consistent with that measured directly from the absorption lines of the white dwarf (Long and Gilliland 1999). This implies that the three-body approximation is essential for correct description of the outer parts of the disk. Wings of the emission lines profiles are likely to be contaminated by contributions from parts of the stream which are overflowing the disk close to the white dwarf. Radial velocities measured from wings (Kraft 1962, Stover 1981), analyzed only in phase intervals free of contamination, give K1 consistent with other determinations. New analysis of the spot eclipses gives i=69°±2° and shows that during outburst the disk expands up to about rd≈0.40-0.45≈0.9 rRoche, while during quiescence it contracts from rd≈0.75 rRoche to rd≈0.65 rRoche. However, the radius of the disk during quiescence obtained from Vdsin i appears larger: rd≈0.85-0.95 rRoche. System parameters are: M1=1.07±0.08 Msolar, M2=0.39±0.02 Msolar, R1=4.7±0.7×108 cm, R2=0.45±0.01 Rsolar, and distance d=96±4 pc. The radius of the secondary component, when compared with its mass, shows that the secondary is a normal main sequence star.