EXOPLINES: Molecular Absorption Cross-Section Database for Brown Dwarf and Giant Exoplanet Atmospheres

Abstract

Stellar, substellar, and planetary atmosphere models are all highly sensitive to the input opacities. Generational differences between various state-of-the-art stellar/planetary models are primarily because of incomplete and outdated atomic/molecular line-lists. Here we present a database of precomputed absorption cross-sections for all isotopologues of key atmospheric molecules relevant to latetype stellar, brown dwarf, and planetary atmospheres: MgH, AlH, CaH, TiH, CrH, FeH, SiO, TiO, VO, and H 2 O. The pressure and temperature ranges of the computed opacities are between 10 −6 -3000 bar and 75-4000 K, and their spectral ranges are 0.25-330 µm for many cases where possible. For cases with no pressure-broadening data, we use collision theory to bridge the gap. We also probe the effect of absorption cross-sections calculated from different line lists in the context of Ultra-Hot Jupiter and M-dwarf atmospheres. Using 1-D self-consistent radiative-convective thermochemical equilibrium models, we report significant variations in the theoretical spectra and thermal profiles of substellar atmospheres. With a 2000 K representative Ultra-Hot Jupiter, we report variations of up to 320 and 80 ppm in transmission and thermal emission spectra, respectively. For a 3000 K M-dwarf, we find differences of up to 125% in the spectra. We find that the most significant differences arise due to the choice of TiO line-lists, primarily below 1µm. In sum, we present (1) a database of pre-computed molecular absorption cross-sections, and (2) quantify biases that arise when characterizing substellar/exoplanet atmospheres due to line list differences, therefore highlighting the importance of correct and complete opacities for eventual applications to high precision spectroscopy and photometry.

A solar C/O and sub-solar metallicity in a hot Jupiter atmosphere

“…When we refer to "CO" constraints in the main text, we refer to the main isotopologue, 12 C 16 O. Cross-sections are computed with the HELIOS-K package 44,45 at 0.001 cm −1 resolution and a Voigt wing cut of 100 cm −1 and then interpolated down to a constant R=250K. For water we use the POKOZATEL 46 line list with methods/broadening parameters described in 47 . ED Fig.…”