HORuS transmission spectroscopy of 55 Cnc e

TL;DR

This paper presents initial observations of the super-Earth 55 Cnc e using the HORuS spectrograph, setting new upper limits on atmospheric sodium and demonstrating HORuS's potential for planetary transmission spectroscopy.

Contribution

First use of HORuS spectrograph for exoplanet transmission spectroscopy, achieving high sensitivity and setting stringent upper limits on atmospheric features of 55 Cnc e.

Findings

Set an upper limit on Na I absorption in 55 Cnc e's atmosphere

Demonstrated HORuS reaches photon-noise limit for transmission spectra

Showed HORuS can detect atmospheres of larger planets

Abstract

The High Optical Resolution Spectrograph (HORuS) is a new high-resolution echelle spectrograph available on the 10.4 m Gran Telescopio Canarias (GTC). We report on the first HORuS observations of a transit of the super-Earth planet 55 Cnc e. We investigate the presence of Na I and H$\alpha$ in its transmission spectrum and explore the capabilities of HORuS for planetary transmission spectroscopy. Our methodology leads to residuals in the difference spectrum between the in-transit and out-of-transit spectra for the Na I doublet lines of (3.4 $\pm$ 0.4) $\times$ 10$^{-4}$, which sets an upper limit to the detection of line absorption from the planetary atmosphere that is one order of magnitude more stringent that those reported in the literature. We demonstrate that we are able to reach the photon-noise limit in the residual spectra using HORuS to a degree that we would be able to easily detect giant planets with larger atmospheres. In addition, we modelled the structure, chemistry and transmission spectrum of 55 Cnc e using state-of-the-art open source tools.