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1

Enhanced Mass Transfer in U Geminorum during its Outbursts and Superoutburst

Smak J.

Acta Astronomica

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2005

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Vol. 55, No. 3

315--320

EN

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.

2

The 1985 Superoutburst of U Geminorum. Detection of Superhumps

Smak J., Waagen E. O.

Acta Astronomica

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2004

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Vol. 54, No. 4

433--442

EN

Superhumps are detected in the AAVSO light curve of the 1985 superoutbursts of U Gem. They appeared not later than 2-3 days after reaching maximum and disappeared not later than about 4 days before the final decline. The superhump period was Psh≈0.20 d and increased at a rate of dP/dt≈2×10-4. The corresponding superhump period excess was ε=0.130±0.014. The full amplitude of the superhumps was 2A≈0.3 mag. During the last ten days of the superoutburst additional periodic variations were also present. Their period was ≈0.18 d and their full amplitude grew from 2A≈0.2 mag to ≈0.5 mag. U Gem, together with the permanent superhumper TV Col (Retter et al. 2003), form a challenge to the theory which is unable to explain superoutburst and superhumps in systems with long orbital periods and mass ratios q>qcrit=1/3. Another challenge to the theory comes from a comparison of the theoretical ε-q relation resulting from numerical simulations (Murray 2000) with its observational counterpart: for q>0.15 the model values of ε are systematically - by a factor of 2 - too large.

3

U Gem - Rediscussion of Radial Velocities and System Parameters

Smak J.

Acta Astronomica

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2001

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Vol. 51, No. 3

279--293

EN

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.

4

On the Interpretation of Doppler Tomograms of Dwarf Nova Disks During Outbursts

Smak J.

Acta Astronomica

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2001

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Vol. 51, No. 3

295--302

EN

Simple model of the disk based on purely mechanical, restricted three-body approximation is already sufficient to explain the presence and shapes of the two arch-like structures observed in Doppler tomograms of dwarf nova disks during their outbursts. In particular, it explains their non-equal intensities (which could not be explained by the 2D hydrodynamic, spiral-wave models).