The GAPS Programme at TNG

Abstract

Context. The analysis of exoplanetary atmospheres by means of high-resolution spectroscopy is an expanding research field which provides information on the chemical composition, thermal structure, atmospheric dynamics, and orbital velocity of exoplanets. Aims. In this work, we aim to detect the light reflected by the exoplanet 51 Peg b by employing optical high-resolution spectroscopy. Methods. To detect the light reflected by the planetary dayside, we used optical High Accuracy Radial velocity Planet Searcher and High Accuracy Radial velocity Planet Searcher for the Northern hemisphere spectra taken near the superior conjunction of the planet, when the flux contrast between the planet and the star is maximum. To search for the weak planetary signal, we cross-correlated the observed spectra with a high signal-to-noise ratio stellar spectrum. Results. We homogeneously analyze the available datasets and derive a 10−5 upper limit on the planet-to-star flux contrast in the optical. Conclusions. The upper limit on the planet-to-star flux contrast of 10−5 translates into a low albedo of the planetary atmosphere (Ag ≲ 0.05−0.15 for an assumed planetary radius in the range of 1.5−0.9 RJup, as estimated from the planet’s mass).