The Transit Light Curve Project. IX. Evidence for a Smaller Radius of the Exoplanet XO-3b

TL;DR

This study refines the radius measurement of exoplanet XO-3b using transit photometry, favoring a smaller radius than previous estimates, and discusses implications for planetary models and future observations.

Contribution

The paper provides a more precise radius estimate for XO-3b and addresses discrepancies between different stellar density measurements, revising system parameters accordingly.

Findings

Planetary radius is 1.217 +/- 0.073 R_Jup.

The radius is about 1 sigma larger than theoretical predictions.

Refined transit and occultation ephemerides are provided.

Abstract

We present photometry of 13 transits of XO-3b, a massive transiting planet on an eccentric orbit. Previous data led to two inconsistent estimates of the planetary radius. Our data strongly favor the smaller radius, with increased precision: R_p = 1.217 +/- 0.073 R_Jup. A conflict remains between the mean stellar density determined from the light curve, and the stellar surface gravity determined from the shapes of spectral lines. We argue the light curve should take precedence, and revise the system parameters accordingly. The planetary radius is about 1 sigma larger than the theoretical radius for a hydrogen-helium planet of the given mass and insolation. To help in planning future observations, we provide refined transit and occultation ephemerides.