PTFO 8-8695b represents the first transiting exoplanet candidate orbiting a pre-main-sequence star ( ) .
We find that the unusual lightcurve shapes of PTFO 8-8695 can be explained by transits of a planet across an oblate , gravity-darkened stellar disk .
We develop a theoretical framework for understanding precession of a planetary orbit ’ s ascending node for the case when the stellar rotational angular momentum and the planetary orbital angular momentum are comparable in magnitude .
We then implement those ideas to simultaneously and self-consistently fit two separate lightcurves observed in 2009 December and 2010 December .
Our two self-consistent fits yield M _ { p } = 3.0 ~ { } \mathrm { M _ { Jup } } and M _ { p } = 3.6 ~ { } \mathrm { M _ { Jup } } for assumed stellar masses of M _ { * } = 0.34 ~ { } \mathrm { M _ { \odot } } and M _ { * } = 0.44 ~ { } \mathrm { M _ { \odot } } respectively .
The two fits have precession periods of 293 days and 581 days .
These mass determinations ( consistent with previous upper limits ) along with the strength of the gravity-darkened precessing model together validate PTFO 8-8695b as just the second Hot Jupiter known to orbit an M-dwarf .
Our fits show a high degree of spin-orbit misalignment in the PTFO 8-8695 system : 69 ^ { \circ } \pm 2 ^ { \circ } or 73.1 ^ { \circ } \pm 0.5 ^ { \circ } , in the two cases .
The large misalignment is consistent with the hypothesis that planets become Hot Jupiters with random orbital plane alignments early in a system ’ s lifetime .
We predict that as a result of the highly misaligned , precessing system , the transits should disappear for months at a time over the course of the system ’ s precession period .
The precessing , gravity-darkened model also predicts other observable effects : changing orbit inclination that could be detected by radial velocity observations , changing stellar inclination that would manifest as varying v \sin i , changing projected spin-orbit alignment that could be seen by the Rossiter-McLaughlin effect , changing transit shapes over the course of the precession , and differing lightcurves as a function of wavelength .
Our measured planet radii of 1.64 ~ { } \mathrm { R _ { Jup } } and 1.68 ~ { } \mathrm { R _ { Jup } } in each case are consistent with a young , hydrogen-dominated planet that results from a ‘ hot-start ’ formation mechanism .