TrES-4: A Transiting Hot Jupiter of Very Low Density

TL;DR

This paper reports the discovery and characterization of TrES-4, a highly inflated hot Jupiter with the lowest density among known transiting exoplanets, challenging existing models of planetary structure.

Contribution

It presents the first detailed analysis of TrES-4, including its mass, radius, and density, highlighting its extreme physical properties and implications for hot Jupiter models.

Findings

TrES-4 has the largest radius among known transiting planets.

It has the lowest density of any transiting exoplanet.

The planet's properties challenge current models of hot Jupiter structure.

Abstract

We report the discovery of TrES-4, a hot Jupiter that transits the star GSC 02620-00648 every 3.55 days. From high-resolution spectroscopy of the star we estimate a stellar effective temperature of Teff = 6100 +/- 150 K, and from high-precision z and B photometry of the transit we constrain the ratio of the semi-major axis and the stellar radius to be a/R = 6.03 +/- 0.13. We compare these values to model stellar isochrones to constrain the stellar mass to be M* = 1.22 +/- 0.17 Msun. Based on this estimate and the photometric time series, we constrain the stellar radius to be R* = 1.738 +/- 0.092 Rsun and the planet radius to be Rp = 1.674 +/- 0.094 RJup. We model our radial-velocity data assuming a circular orbit and find a planetary mass of 0.84 +/- 0.10 MJup. Our radial-velocity observations rule out line-bisector variations that would indicate a specious detection resulting from a blend of an eclipsing binary system. TrES-4 has the largest radius and lowest density of any of the known transiting planets. It presents a challenge to current models of the physical structure of hot Jupiters, and indicates that the diversity of physical properties amongst the members of this class of exoplanets has yet to be fully explored.