Empirical line lists and absorption cross sections for methane at high temperature

TL;DR

This study provides the first high-resolution laboratory absorption spectra of hot methane at temperatures up to 1200 K, validating theoretical models and improving understanding of methane's spectral behavior in high-temperature environments.

Contribution

It presents empirical line lists and continua for hot methane, bridging the gap between theoretical predictions and observational data at elevated temperatures.

Findings

Confirmed the continuum formation from weak absorption lines at high temperatures

Provided empirical spectra that match brown dwarf observations

Highlighted discrepancies between theory and experiment in hot methane spectra

Abstract

Hot methane is found in many "cool" sub-stellar astronomical sources including brown dwarfs and exoplanets, as well as in combustion environments on Earth. We report on the first high-resolution laboratory absorption spectra of hot methane at temperatures up to 1200 K. Our observations are compared to the latest theoretical spectral predictions and recent brown dwarf spectra. The expectation that millions of weak absorption lines combine to form a continuum, not seen at room temperature, is confirmed. Our high-resolution transmittance spectra account for both the emission and absorption of methane at elevated temperatures. From these spectra, we obtain an empirical line list and continuum that is able to account for the absorption of methane in high temperature environments at both high and low resolution. Great advances have recently been made in the theoretical prediction of hot methane, and our experimental measurements highlight the progress made and the problems that still remain.