The spectrum of hot methane in astronomical objects using a comprehensive computed line list

TL;DR

This paper introduces a comprehensive methane line list, 10to10, with nearly 10 billion transitions, significantly improving atmospheric models of brown dwarfs and exoplanets by providing more accurate spectral data at high temperatures.

Contribution

A new, extensive methane line list covering a broad spectral range, enabling more accurate modeling of hot astronomical objects at elevated temperatures.

Findings

Better agreement with brown dwarf observations using 10to10.

Up to twentyfold increase in methane abundance estimates for exoplanet HD 189733b.

Highlighting the importance of hot transition inclusion for atmospheric characterization.

Abstract

Hot methane spectra are important in environments ranging from flames to the atmospheres of cool stars and exoplanets. A new spectroscopic line list, 10to10, for $^{12}$CH$_4$ containing almost 10 billion transitions is presented. This comprehensive line list covers a broad spectroscopic range and is applicable for temperatures up to 1 500 K. Previous methane data are incomplete leading to underestimated opacities at short wavelengths and elevated temperatures. Use of 10to10 in models of the bright T4.5 brown dwarf 2MASS 0559-14 leads to significantly better agreement with observations and in studies of the hot Jupiter exoplanet HD 189733b leads to up to a twentifold increase in methane abundance. It is demonstrated that proper inclusion of the huge increase in hot transitions which are important at elevated temperatures is crucial for accurate characterizations of atmospheres of brown dwarfs and exoplanets, especially when observed in the near-infrared.