The GTC exoplanet transit spectroscopy survey. IV.: No asymmetries in the transit of Corot-29b

TL;DR

This study re-examined the asymmetric transit of CoRoT-29b with high-precision spectro-photometry and found no asymmetry in recent observations, suggesting the original asymmetry was either time-dependent or due to instrumental effects.

Contribution

The paper provides the first high-precision, multi-epoch observations that challenge previous reports of transit asymmetry in CoRoT-29b, indicating the asymmetry may not be intrinsic.

Findings

No asymmetry detected in 2014 and 2015 transits

No evidence of color-dependent transit features

Previous asymmetry may have been time-dependent or instrumental

Abstract

Context. The launch of the exoplanet space missions obtaining exquisite photometry from space has resulted in the discovery of thousands of planetary systems with very different physical properties and architectures. Among them, the exoplanet CoRoT-29b was identified in the light curves the mission obtained in summer 2011, and presented an asymmetric transit light curve, which was tentatively explained via the effects of gravity darkening. Aims. Transits of CoRoT-29b are measured with precision photometry, to characterize the reported asymmetry in their transit shape. Methods. Using the OSIRIS spectrograph at the 10-m GTC telescope, we perform spectro-photometric differential observations, which allow us to both calculate a high-accuracy photometric light curve, and a study of the color-dependence of the transit. Results. After careful data analysis, we find that the previously reported asymmetry is not present in either of two transits, observed in July 2014 and July 2015 with high photometric precisions of 300ppm over 5 minutes. Due to the relative faintness of the star, we do not reach the precision necessary to perform transmission spectroscopy of its atmosphere, but we see no signs of color-dependency of the transit depth or duration. Conclusions. We conclude that the previously reported asymmetry may have been a time-dependent phenomenon, which did not occur in more recent epochs. Alternatively, instrumental effects in the discovery data may need to be reconsidered.