Detection of a planetary system orbiting the eclipsing polar HU Aqr

ABSTRACT Using the precise times of mid‐egress of the eclipsing polar HU Aqr, we discovered that this polar is orbited by two or more giant planets. The two planets detected so far have masses of at least 5.9 and 4.5MJup. Their respective distances from the polar are 3.6 and 5.4 au with periods of 6.54 and 11.96 yr, respectively. The observed rate of decrease of period derived from the downward parabolic change in the observed − calculated (O − C) curve is a factor of 15 larger than the value expected for gravitational radiation. This indicates that it may be only a part of a long‐period cyclic variation, revealing the presence of one more planet. It is interesting to note that the two detected circumbinary planets follow the Titus–Bode law of solar planets with n= 5 and 6. We estimate that another 10 yr of observations will reveal the presence of the predicted third planet.