Eclipse Timing of the Eccentric Planet HD 80606b with JWST: Constraints on a Second Planet and other Dynamical Effects

Abstract

A variety of effects can perturb the orbital properties of single planets in close orbits around their host stars. HD80606 b is a highly eccentric ($\epsilon$=0.93) exoplanet orbiting its host G5V star, HD80606. HD80606 b became a compelling target for exoplanet research after (Laughlin et al 2009) discovered that the 4.16 MJup planet transits and is eclipsed by HD80606, thereby enabling photometric and spectroscopic observations to yield a wealth of information about the object. The exquisite precision of recent JWST eclipse timing offers an opportunity to investigate whether the orbit of HD80606 b is modified due to a variety of mechanisms, including General Relativity, tidal torques, or the presence of a second perturbing planet. We have used over 25 years of radial velocity data plus eclipse and transit observations to place limits on the precession of HD80606 b's orbit and to assess which of these effects, if any, are observable. The new models are consistent with constant values of period, eccentricity and the argument of periastron, $\omega$, with a limit on $\dot{\omega}$ at the level of the predicted GR drift. The PRV and timing data limit the mass and location of a second planet external to HD80606b. Timing offsets between JWST eclipses relative to the Pearson et al (2022) predictions are attributed to the poor constraints on $\sqrt{\epsilon} (\cos\ \omega, \sin\ \omega)$ with only the single eclipse measurement available (Spitzer 2009) in that analysis and to an over-weighting of the eclipse timing in that earlier analysis.