The 1985 Superoutburst of U Geminorum. Detection of Superhumps

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.