PNAS2014-07-10 5:24 PM

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

Significance
Hot methane is important in cool stars, brown dwarfs, exoplanets, gas turbine engines, and elsewhere. There is a pressing need for an accurate and complete spectroscopic database for methane at elevated temperatures. We present a comprehensive spectroscopic line list for methane containing almost 10 billion transitions, 2,000 times more than any previous compilation, covering a broad spectroscopic range and applicable for temperatures up to 1,500 K. We demonstrate that such a line list is essential for correctly modeling the brown dwarf 2MASS 0559-14 and leads to large changes in exoplanet models. We believe that this line list will have a large effect on the field of exoplanets and cool stars.

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 12CH4 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 20-fold 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.

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http://www.pnas.org/content/111/26/9379

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