UCL Discovery

## Detection of an atmosphere around the super-Earth 55 Cancri e

Tsiaras, A; Rocchetto, M; Waldmann, IP; Venot, O; Varley, R; Morello, G; Damiano, M; ... Tennyson, J; + view all (2016) Detection of an atmosphere around the super-Earth 55 Cancri e. Astrophysical Journal , 820 (2) , Article 99. 10.3847/0004-637X/820/2/99.

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1511.08901v2.pdf - Accepted version

## Abstract

We report the analysis of two new spectroscopic observations of the super-Earth 55 Cancri e, in the near infrared, obtained with the WFC3 camera onboard the HST. 55 Cancri e orbits so close to its parent star, that temperatures much higher than 2000 K are expected on its surface. Given the brightness of 55 Cancri, the observations were obtained in scanning mode, adopting a very long scanning length and a very high scanning speed. We use our specialized pipeline to take into account systematics introduced by these observational parameters when coupled with the geometrical distortions of the instrument. We measure the transit depth per wavelength channel with an average relative uncertainty of 22 ppm per visit and find modulations that depart from a straight line model with a 6$\sigma$ confidence level. These results suggest that 55 Cancri e is surrounded by an atmosphere, which is probably hydrogen-rich. Our fully Bayesian spectral retrieval code, T-REx, has identified HCN to be the most likely molecular candidate able to explain the features at 1.42 and 1.54 $\mu$m. While additional spectroscopic observations in a broader wavelength range in the infrared will be needed to confirm the HCN detection, we discuss here the implications of such result. Our chemical model, developed with combustion specialists, indicates that relatively high mixing ratios of HCN may be caused by a high C/O ratio. This result suggests this super-Earth is a carbon-rich environment even more exotic than previously thought.

Type: Article Detection of an atmosphere around the super-Earth 55 Cancri e An open access version is available from UCL Discovery 10.3847/0004-637X/820/2/99 http://iopscience.iop.org/article/10.3847/0004-637... English Copyright © 2016. The American Astronomical Society. All rights reserved. This is an author's manuscript version of an article accepted for publication in the Astrophysical Journal. methods: data analysis; planets and satellites: atmospheres; planets and satellites: individual (55 Cancri e), spectral retrieval; techniques: spectroscopic UCL > Provost and Vice Provost OfficesUCL > Provost and Vice Provost Offices > UCL BEAMSUCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical SciencesUCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy https://discovery.ucl.ac.uk/id/eprint/1474886