The GAPS Programme at TNG. XXIX. No detection of reflected light from 51 Peg b using optical high-resolution spectroscopy

TL;DR

This study used high-resolution optical spectroscopy to search for reflected light from exoplanet 51 Peg b but found no detection, setting an upper limit on its brightness and albedo.

Contribution

First homogeneous analysis of optical high-resolution spectra for 51 Peg b to constrain its reflected light and albedo.

Findings

No reflected light detected, upper limit of 10^-5 on flux contrast.

Derived low planetary albedo, A_g less than 0.05-0.15.

Set constraints on the planet's atmospheric properties.

Abstract

The analysis of exoplanetary atmospheres by means of high-resolution spectroscopy is an expanding research field which provides information on chemical composition, thermal structure, atmospheric dynamics and orbital velocity of exoplanets. In this work, we aim at the detection of the light reflected by the exoplanet 51~Peg~b employing optical high-resolution spectroscopy. To detect the light reflected by the planetary dayside we use optical HARPS and HARPS-N 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-correlate the observed spectra with a high S/N stellar spectrum. We homogeneously analyze the available datasets and derive a $10^{-5}$ upper limit on the planet-to-star flux contrast in the optical. The upper limit on the planet-to-star flux contrast of $10^{-5}$ translates into a low albedo of the planetary atmosphere ($\rm A_g\lesssim0.05-0.15$ for an assumed planetary radius in the range $\rm 1.5-0.9~R_{Jup}$, as estimated from the planet's mass).