Kepler-11 is a Solar Twin: Revising the Masses and Radii of Benchmark Planets Via Precise Stellar Characterization

TL;DR

This study precisely characterizes the Kepler-11 star, revises the planetary densities upward, and discusses the implications for understanding low-density exoplanets, using high-quality spectroscopy and photodynamical modeling.

Contribution

It provides the first detailed stellar parameters and chemical composition of Kepler-11, leading to revised, higher planetary densities and insights into their nature.

Findings

Kepler-11 is a young solar twin with higher metallicity.

Planet densities are increased by 20-95%, making them more typical of 'puffy' exoplanets.

Analysis reveals a tension between spectroscopic and transit-based stellar density estimates.

Abstract

The six planets of the Kepler-11 system are the archetypal example of a population of surprisingly low-density transiting planets revealed by the Kepler mission. We have determined the fundamental parameters and chemical composition of the Kepler-11 host star to unprecedented precision using an extremely high quality spectrum from Keck-HIRES (R$\simeq$67,000, S/N per pixel$\simeq$260 at 600 nm). Contrary to previously published results, our spectroscopic constraints indicate that Kepler-11 is a young main-sequence solar twin. The revised stellar parameters and new analysis raise the densities of the Kepler-11 planets by between 20-95% per planet, making them more typical of the emerging class of "puffy" close-in exoplanets. We obtain photospheric abundances of 22 elements and find that Kepler-11 has an abundance pattern similar to that of the Sun with a slightly higher overall metallicity. We additionally analyze the Kepler lightcurves using a photodynamical model and discuss the tension between spectroscopic and transit/TTV-based stellar density estimates.