A reappraisal of parameters for the putative planet PTFO 8-8695b and its potentially precessing parent star

TL;DR

This study reevaluates the planetary hypothesis for PTFO 8-8695b by modeling stellar effects, finding inconsistencies with observations that challenge the exoplanet interpretation.

Contribution

It introduces improved stellar modeling techniques and demonstrates that the observed fading events are unlikely caused by a transiting planet.

Findings

Gravity darkening models require near-critical stellar rotation.

Predicted stellar precession variability contradicts observations.

Orbital and rotational angular momentum ratios are physically implausible.

Abstract

Published photometry of fading events in the PTFO 8-8695 system is modelled using improved treatments of stellar geometry, surface intensities, and, particularly, gravity darkening, with a view to testing the planetary-transit hypothesis. Variability in the morphology of fading events can be reproduced by adopting convective-envelope gravity darkening, but near-critical stellar rotation is required. This leads to inconsistencies with spectroscopic observations; the model also predicts substantial photometric variability associated with stellar precession, contrary to observations. Furthermore, the empirical ratio of orbital to rotational angular momenta is at odds with physically plausible values. An exoplanet transiting a precessing, gravity-darkened star may not be the correct explanation of periodic fading events in this system.