Circumbinary Planets Around Evolved Stars

Abstract

The current state of evidence for planets around evolved star binaries is reviewed. Sharp eclipse features from compact evolved stars in binaries enable exquisite measurements of eclipse times which in principle are sensitive enough to detect the perturbations due to a circumbinary planet in a Jupiter-like orbit having less than % of Jupiter’s mass. Significant eclipse time perturbations have been measured in over 30 systems. Planetary orbits have been proposed for ten of these, six of them requiring two or more planets to fit the observed variations. The present picture is however confused, with several proposed orbits failing in the light of new data or proving to be dynamically unstable. Internal structural changes of the component stars are a probable source of the noise in these measurements, although proposed mechanisms struggle to explain the magnitude of the timing variations seen in several systems. Future progress requires sources of guaranteed timing stability. Some have already been found, and many more can be expected from current and future variability surveys.