2014MNRAS.437..475M

We present 25 new eclipse times of the white dwarf binary NN Ser taken with the high-speed camera ULTRACAM on the William Herschel Telescope and New Technology Telescope, the RISE camera on the Liverpool Telescope and HAWK-I on the Very Large Telescope to test the two-planet model proposed to explain variations in its eclipse times measured over the last 25yr. The planetary model survives the test with flying colours, correctly predicting a progressive lag in eclipse times of 36s that has set in since 2010 compared to the previous 8yr of precise times. Allowing both orbits to be eccentric, we find orbital periods of 7.9±0.5 and 15.3±0.3yr, and masses of 2.3±0.5 and 7.3±0.3MJ. We also find dynamically long-lived orbits consistent with the data, associated with 2:1 and 5:2 period ratios. The data scatter by 0.07s relative to the best-fitting model, by some margin the most precise of any of the proposed eclipsing compact object planet hosts. Despite the high precision, degeneracy in the orbit fits prevents a significant measurement of a period change of the binary and of N-body effects. Finally, we point out a major flaw with a previous dynamical stability analysis of NN Ser, and by extension, with a number of analyses of similar systems.