Seminar

The occurrence rate of circumstellar planets in binary star systems is notably suppressed due to gravitational perturbation of close stellar companions. Nevertheless, a planet around the primary star has been found midway between the two stellar components of  Octantis characterised by an exceptionally small orbital semimajor axis of 2.6 AU. The formidable geometry leaves a retrograde planetary orbit the only option for dynamical stability, which must be explained by any scenario for the planet’s origin. The situation is further complicated by stellar evolution as the secondary star is very likely a white dwarf, implying that the binary and its orbit have significantly evolved. Despite the theoretical challenges, all standard observational tests have ruled out any non-planetary alternatives. Hence, my research attempts to lend theoretical ground to the origin of the Octantis planet. Nested sampling and a rapid binary stellar evolution code have been utilised to explore plausible primordial settings of Octantis. N-body simulations incorporated with the effects of binary stellar evolution will be performed to examine the dynamical evolution of the planet. This study is anticipated to show whether a planet that formed with the binary can evolved into its current orbit. If not, the planet could be a second-generation planet that formed from the expelled material of an evolving star.

Additional information: Mr. Ho Wan CHENG, howan1da@connect.hku.hk