High-resolution spectroscopic search for the thermal emission of the extrasolar planet HD 217107 b

TL;DR

This study used high-resolution spectroscopy to search for thermal emission from exoplanet HD 217107 b, aiming to determine its orbital inclination, mass, and flux ratio, but did not detect the planet, providing sensitivity limits and strategies for future observations.

Contribution

The paper refines a correlation method for detecting non-transiting exoplanets via high-resolution spectra and assesses its sensitivity, offering improved observational strategies for future atmospheric detection.

Findings

Planet-to-star flux ratio constrained to < 5 x 10^-3 at 3-sigma confidence

No detection of the planet's thermal emission with current data

Simulations suggest optimized strategies can improve future detection prospects

Abstract

We analyzed the combined near-infrared spectrum of a star-planet system with thermal emission atmospheric models, based on the composition and physical parameters of the system. The main objective of this work is to obtain the inclination of the orbit, the mass of the exoplanet, and the planet-to-star flux ratio. We present the results of our routines on the planetary system HD 217107, which was observed with the high-resolution spectrograph Phoenix at 2.14 microns. We revisited and tuned a correlation method to directly search for the high-resolution signature of a known non-transiting extrasolar planet. We could not detect the planet with our current data, but we present sensitivity estimates of our method and the respective constraints on the planetary parameters. With a confidence level of 3--$\sigma$ we constrain the HD 217107 b planet-to-star flux ratio to be less than $5 \times 10^{-3}$. We also carried out simulations on other planet candidates to assess the detectability limit of atmospheric water on realistically simulated data sets for this instrument, and we outline an optimized observational and selection strategy to increase future probabilities of success by considering the optimal observing conditions and the most suitable candidates.