Large Binocular Telescope view of the atmosphere of GJ1214b

TL;DR

This study uses simultaneous multi-wavelength transit observations and stellar activity monitoring to confirm that GJ1214b has a cloudy atmosphere with a flat transmission spectrum, resolving previous conflicting data.

Contribution

First simultaneous optical measurements of GJ1214b's radius at different wavelengths, combined with stellar activity correction, to clarify its atmospheric properties.

Findings

Confirmed a flat transmission spectrum for GJ1214b

Detected a longer stellar rotation period

Supported the cloudy atmosphere hypothesis

Abstract

The atmospheric composition and vertical structure of the super-Earth GJ1214b has been a subject of debate since its discovery in 2009. Recent studies have indicated that high-altitude clouds might mask the lower layers. However, some data points that were gathered at different times and facilities do not fit this picture, probably because of a combination of stellar activity and systematic errors. We observed two transits of GJ1214b with the Large Binocular Camera, the dual-channel camera at the Large Binocular Telescope. For the first time, we simultaneously measured the relative planetary radius $k=R_\mathrm{p}/R_\star$ at blue and red optical wavelengths ($B+R$), thus constraining the Rayleigh scattering on GJ1214b after correcting for stellar activity effects. To the same purpose, a long-term photometric follow-up of the host star was carried out with WiFSIP at STELLA, revealing a rotational period that is significantly longer than previously reported. Our new unbiased estimates of $k$ yield a flat transmission spectrum extending to shorter wavelengths, thus confirming the cloudy atmosphere scenario for GJ1214b.