The Water Abundance of the Directly Imaged Substellar Companion {\kappa} And b Retrieved from a Near Infrared Spectrum

TL;DR

This study applies spectral retrieval to near-infrared data of the directly imaged substellar companion {ppa} And b, estimating its water vapor abundance and providing insights into its atmospheric composition and formation history.

Contribution

It presents the first detailed spectral retrieval analysis of {ppa} And b's atmosphere using a Markov Chain Monte Carlo approach on near-infrared spectra.

Findings

Water vapor abundance estimated with uncertainties

Upper limit placed on methane abundance

Comparison with hot Jupiter and other directly imaged planet studies

Abstract

Spectral retrieval has proven to be a powerful tool for constraining the physical properties and atmospheric compositions of extrasolar planet atmospheres from observed spectra, primarily for transiting objects but also for directly imaged planets and brown dwarfs. Despite its strengths, this approach has been applied to only about a dozen targets. Determining the abundances of the main carbon and oxygen-bearing compounds in a planetary atmosphere can lead to the C/O ratio of the object, which is crucial in understanding its formation and migration history. We present a retrieval analysis on the published near-infrared spectrum of {\kappa} And b, a directly imaged substellar companion to a young B9 star. We fit the emission spectrum model utilizing a Markov Chain Monte Carlo algorithm. We estimate the abundance of water vapor, and its uncertainty, in the atmosphere of the object. In addition, we place an upper limit on the abundance of CH$_4$. We compare qualitatively our results to studies that have applied model retrieval on multiband photometry and emission spectroscopy of hot Jupiters (extrasolar giant planets with orbital periods of several days) and the directly imaged giant planet HR 8799b.