New H2 collision-induced absorption and NH3 opacity and the spectra of the coolest brown dwarfs

TL;DR

This paper introduces improved atmospheric models for brown dwarfs using new ammonia and hydrogen collision-induced absorption data, leading to better spectral fits and insights into the spectral features of the coolest brown dwarfs.

Contribution

The paper provides updated model atmospheres with new NH3 and H2 opacity data, enhancing spectral fitting accuracy for late T and Y dwarfs.

Findings

Improved spectral fits for the T7p dwarf Gliese 570D.

Identification of NH3 absorption features in very late T and Y dwarfs.

Detailed analysis of NH3 features in the T9/T10 dwarf spectrum.

Abstract

We present new cloudy and cloudless model atmospheres for brown dwarfs using recent ab initio calculations of the line list of ammonia (NH3) and of the collision-induced absorption of molecular hydrogen (H2). We compare the new synthetic spectra with models based on an earlier description of the H2 and NH3 opacities. We find a significant improvement in fitting the nearly complete spectral energy distribution of the T7p dwarf Gliese 570D and in near infrared color-magnitude diagrams of field brown dwarfs. We apply these new models to the identification of NH3 absorption in the H band peak of very late T dwarfs and the new Y dwarfs and discuss the observed trend in the NH3-H spectral index. The new NH3 line list also allows a detailed study of the medium resolution spectrum of the T9/T10 dwarf UGPS J072227.51-054031.2 where we identify several specific features caused by NH3.