The Transit Light Curve Project. X. A Christmas Transit of HD 17156b

TL;DR

This paper reports detailed photometric and spectroscopic observations of the December 25, 2007 transit of exoplanet HD 17156b, refining its system parameters and discussing implications for planetary composition and orbital dynamics.

Contribution

It provides the first combined photometric and radial velocity analysis of HD 17156b's transit, refining its mass, radius, and orbital parameters with high precision.

Findings

Planet's mass: 3.212 Jupiter masses

Planet's radius: 1.023 Jupiter radii

No evidence of orbital perturbations

Abstract

Photometry is presented of the Dec. 25, 2007 transit of HD 17156b, which has the longest orbital period and highest orbital eccentricity of all the known transiting exoplanets. New measurements of the stellar radial velocity are also presented. All the data are combined and integrated with stellar-evolutionary modeling to derive refined system parameters. The planet's mass and radius are found to be 3.212_{-0.082}^{+0.069} Jupiter masses and 1.023_{-0.055}^{+0.070} Jupiter radii. The corresponding stellar properties are 1.263_{-0.047}^{+0.035} solar masses and 1.446_{-0.067}^{+0.099} solar radii. The planet is smaller by 1 sigma than a theoretical solar-composition gas giant with the same mass and equilibrium temperature, a possible indication of heavy-element enrichment. The midtransit time is measured to within 1 min, and shows no deviation from a linear ephemeris (and therefore no evidence for orbital perturbations from other planets). We provide ephemerides for future transits and superior conjunctions. There is an 18% chance that the orbital plane is oriented close enough to edge-on for secondary eclipses to occur at superior conjunction. Observations of secondary eclipses would reveal the thermal emission spectrum of a planet that experiences unusually large tidal heating and insolation variations.