The Sonora Substellar Atmosphere Models. IV. Elf Owl: Atmospheric Mixing and Chemical Disequilibrium with Varying Metallicity and C/O Ratios (Y- type Models)

• Overview

          The Sonora Elf Owl Models is a successor to the Sonora Bobcat and Sonora Cholla models. The Sonora Elf Owl model grid includes cloud-free radiative-convective equilibrium model atmospheres with vertical mixing induced disequilibrium chemistry with sub-solar to super-solar atmospheric metallicities and Carbon-to-Oxygen ratio. The atmospheric models have been computed using the open-source radiative-convective equilibrium model PICASO. The parameters included within this grid are effective temperature (Teff), gravity (log(g)), vertical eddy diffusion coefficient (log(Kzz)), atmospheric metallicity ([M/H]), and Carbon-to-Oxygen ratio (C/O).

The ranges and increments of these parameters are described in the published paper.

• Three grids available on three links

            The model grid has been presented using three Zenodo repositories. This repository has all the models between Teff of 275 to 550 K (applicable to Y-type objects). The models for Teff between 575 to 1200 K (applicable for T- type objects) are available in the Zenodo DOI :- https://zenodo.org/records/10385821. The models for Teff between 1300 to 2400 K (applicable for L- type objects) are available in the Zenodo DOI :-   https://zenodo.org/records/10385987.

•  File types and how to use them

            The models have been presented in the Xarray format so that all the atmospheric properties including the T(P) profile, atmospheric chemistry, and thermal emission spectra can be accessed within the same files. A python based Jupyter notebook named "Reading and plotting Elf Owl Models.ipynb" has been also supplied which demonstrates how to open and use these files.

•   Spectra

            The emission spectra for each atmospheric model has been computed between 0.6 to 15 microns. The reported flux is in the units of erg/s/cm²/cm. Note that these fluxes need to be multiplied with R²/D²  before comparing them with the typically observed flux of brown dwarfs/exoplanets. R is the radius of the object, and D is the distance here.

           As stated in Mukherjee et al. 2023 our CH4 opacity is derived using the Hargreaves et al. 2020 HITEMP line list and computed using the HAPI code (Kochanov et al. 2016). HAPI automatically pre-weights the isotopologues according to earth abundances that are listed on the HITRAN website (see here for CH4). Therefore, users should note that there will be minor features of CH3D included in the models. Given the general absence of deuterated molecules in brown dwarfs  (Teff>~300) we will include a second posting of models which includes the Elf Owl grid with only the major CH4 isotopologue (12C-H4).

          PH3 abundance is treated separately from the general disequilibrium scheme. This is because of the current non-detection of PH3 in many brown dwarf atmospheres (see citations in paper). The current PH3 treatment uses the chemical equilibrium treatment described in Visscher et al. However, after publishing this grid and using the model for analysis of high precision JWST data, we noticed that even the simple chemical equilibrium treatment which reduces the abundance, introduces a noticeable PH3 feature. Therefore in our v2 of this model grid we will further diminish the abundance.