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U Gem - Rediscussion of Radial Velocities and System Parameters

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Smak J.

Acta Astronomica

2001

tom Vol. 51, No. 3

279--293

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.

Enhanced Mass Transfer in U Geminorum during its Outbursts and Superoutburst

75%

Smak J.

Acta Astronomica

2005

tom Vol. 55, No. 3

315--320

The mass transfer rate in U Gem at quiescence, estimated to be M≈1.3-2.0×1016 g/s, is used to calculate the amount of mass ΔMtr transfered to the disk during quiescence. Light curves of U Gem are used to estimate the amounts of mass ΔMaccr accreted during its three types of outbursts. In the case of wide outbursts and the 1985 superoutburst ΔMaccr are much larger than ΔMtr, indicating significant enhancement in the mass transfer by a factor of f≈20-50. There is no evidence for comparable enhancement during narrow outbursts.