The Sonora Substellar Atmosphere Models: Diamondback

OVERVIEW

Presented here are models for non-irradiated, substellar mass objects belonging to the Sonora model series, described in Morley et al. (2024). The files presented here are model temperature-pressure structures with abundances of dominant species ("pressure-temperature_profiles"), emergent spectra from the top of the atmosphere ("spectra"), thermal evolution ("evolution"), synthetic photometry ("photometry"), rainout chemical equilibrium tables used to compute the models ("full_chemistry_tables"). 

Atmospheric structure and spectra file names specify temperature, surface gravity (m/s2), cloud parameterization fsed, metallicity [M/H] and carbon-to-oxygen ratio (C/O) relative to solar. For example, t900g31f1_m-0.5_co1.0 contains the pressure-temperature structure and volume mixing ratios of major molecules (listed in header) for a Teff=900 K, g=31 m/s2, [M/H]=-0.5, and C/O=solar (=0.458). All stated abundances and ratios are relative to Lodders (2010) abundances, see Marley et al. (2021) for details and use caution when referring to other abundance tabulations. The solar C/O ratio in Lodders+2010 is 0.458. 

This particular set of model atmosphere structures and associated spectra, photometry, and evolution, which we name Sonora Diamondback, are for cloudy objects with 3.5 ≤ log g (cgs) ≤ 5.5 and 900 ≤ Teff ≤ 2400K (steps in Teff are 100 K  and steps in log g are 0.5. Models are provided for [M/H] = -0.5, 0.0, and +0.5 and "rainout" chemical equilibrium. For the convenience of having a rectangular table in (T_eff, gravity) space, models are calculated in regimes that are not reached by the evolution, such as very high gravity and very low T_eff. Refer to the companion evolution tables to identify combinations of T_eff and log g outside the bounds covered by the evolution. For other Sonora models that cover different temperature, gravities, metallicities, and disequilibrium chemistry, see Sonora Bobcat, Sonora Cholla, and Sonora Elf Owl. 

ATMOSPHERIC STRUCTURE

Temperature structure files have a one line header denoting the columns of the file.

with P in bar, T in K, and the other values as volume mixing ratios. 

All models have a He mass fraction of 0.28. f_sed is a cloud parameterization (see Ackerman & Marley 2001). 

EVOLUTION

Evolution tables include each of the three metallicities (0.0, +0.5, -0.5) and come in three versions. "nc" denotes cloud-free models for the full evolution. "hybrid" includes clouds (fsed=2) above 1300 K and cloud-free below 1300 K (using the Sonora Bobcat models for T<900 K). "hybrid-grav" includes clouds (fsed=2) that clear between 1000 and 1300 K, with clouds in lower gravity models persisting to colder tempearatures, again using the Sonora Bobcat models for T<900 K.  

PHOTOMETRY

Each model spectrum is complemented with tables of absolute magnitudes in a number of photometric systems commonly used in brown dwarf and exoplanet research (MKO, WISE, Spitzer IRAC, etc).  Magnitudes are computed on the Vega system. 

SPECTRA

The model spectra each contain around 385,000 wavelength points. The resolving power varies with wavelength and ranges from R=6000 to 200000 but is otherwise the same for all spectra (R~6000 from 20-250 microns; R~30,000 from 2-20 microns; R~200,000 for 0.8-2 microns; R~50,000 for 0.3-0.8 microns). The header contains the units and list of molecules included in the radiative transfer calculation. 

Column 1: wavelength in µm

Column 2:  Radiation flux F_ν = 4π x Eddington flux H_ν, in W/m2/m (yes per meter not per micron; also always exercise caution with factors of 4π when comparing to the radiation and Eddington flux, e.g., see Section 3.3 of Hubeny & Mihalas, "Theory of Stellar Atmospheres")

The spectral fluxes are given at the top of the atmosphere and are strictly monochromatic. The model spectrum provides no information in the wavelength range between two tabulated points. Unless a spectral line or feature is well resolved, interpolation in wavelength is not advised.  For comparison with data, the model spectra need to be convolved and binned to the instrumental resolution and sampling. In our experience, a minimum of 10 wavelength points is necessary to obtain a reasonable average flux over a wavelength interval. This is a rule of thumb and caution is advised, especially when comparing with high resolution data. 

CHEMISTRY

We also separately include rainout chemical equilibrium tables for these same atmospheric bulk abundances.Users interested in the chemical abundances of the structure models that are not included in the structure files must interpolate within the matching chemistry file for the atmospheric species of interest.

CLOUDS

The cloud optical properties are also included for each structure/spectrum. The wavelength grid for the cloud calculation is included as a separate file (cloud_wl_grid.txt). Each cloud file contains the level number (matching the structure file), spectral window (matching cloud_wl_grid), optical depth tau, asymmetry paramter g0, and single scattering albedo w0, calculating the scattering using a Henyey-Greenstein phase function. The cloud cross section sigma (in cm2/molecule) is also included. 

CREDITS

If you use these tables in your research, please cite Morley et al. (2024). (https://arxiv.org/abs/2402.00758)