Synthetic Colors for Brown Dwarfs using ATMO Non-Equilibrium Non-Adiabatic Atmospheres

The Tables in the spreadsheets give magnitudes in the Vega system, calculated from synthetic spectra generated by ATMO non-equilibrium non-adiabatic atmospheres (Tremblin et al. 2015, Phillips et al. 2020, Leggett et al. 2021).  Each file has three tabs corresponding to three metallicities: [m/H] = 0, -0.5 and -1.0.  The file 2023_ATMO_MKO_WISE_Spitzer_phot gives MKO Y, J, H, K, Ks, and L'; WISE W1, W2, W3, and W4; and Spitzer [3.6] and [4.5] (columns 5 - 16 in the Tables).  The other three files give colors for JWST NIRCam, NIRISS and MIRI filters, as indicated by the file name.

The photometry is given for an observer at the Earth, for a brown dwarf at 10 pc with a radius of 0.1 Rsun. Column 3 in the Tables give the radius determined by evolutionary models for different metallicities by Marley et al. 2021 (and https://zenodo.org/record/5063476), for the specified temperature and gravity (columns 1 and 2). Column 4 gives the correction to the magnitudes for the correct (theoretical) radius. NOTE THAT THE CORRECTION MUST BE ADDED TO THE MAGNITUDES GIVEN IN COLUMNS 5 - 16 TO OBTAIN THE ABSOLUTE MAGNITUDE.  For an analysis of the model color trends, using a comparison to observations, see Meisner et al. 2023.

The photometry covers the following atmospheric parameters: effective temperatures between 1200 and 250 K (step size 100 K between 1200 and 400 K, with the step size decreasing for lower effective temperatures); log(g) with three values 4.0, 4.5 and 5.0; effective adiabatic index of 1.25; metallicity with three values -1.0, -0.5, and 0. A grid of synthetic spectra was computed at medium resolution (R  ~3000) for wavelengths of 0.2 to 30 microns.  All the models, for a wider range of parameters, are available at https://opendata.erc-atmo.eu. 

The models include rainout of condensates which depletes refractory species, but they do not include clouds. Tremblin et al. 2016 shows that diabatic convective processes (Tremblin et al. 2019) can reduce the temperature gradient in the atmosphere and reproduce the spectral reddening previously explained by clouds. Adjustments to the atmospheric temperature gradient have also been shown to be necessary to reproduce the energy distributions of the coldest brown dwarfs (Leggett et al. 2021). The grids used here modify the temperature gradient by adopting an effective adiabatic index. The levels modified are in between 0.15 and 15 bars at log g = 4.5 and are scaled by ×10^{(log(g)−4.5)} at other surface gravities. Out-of-equilibrium chemistry is used with Kzz = 10⁵ cm²/s at log(g) = 5.0 and is scaled by ×10^{(2(5−log(g)))} at other surface gravities. The mixing length is assumed to be 2 scale heights at 1.5 bars and higher pressures at log(g) = 4.5 and is scaled down by the ratio between the local pressure and the pressure at 1.5 bars for lower pressures. The 1.5 bars limit is scaled by ×10^(log(g)−5) at other surface gravities. The chemistry includes 277 species and out-of-equilibrium chemistry has been performed using the model of Tsai et al. 2017.  Opacity sources include H₂-H₂, H₂-He, H₂O, CO₂, CO, CH₄, NH₃, Na, K, Li, Rb, Cs, TiO, VO, FeH, PH₃, H₂S, HCN, C₂H₂, SO₂, Fe, H^-, and the Rayleigh scattering opacities for H₂, He, CO, N₂, CH₄, NH₃, H₂O, CO₂, H₂S, SO₂.

REFERENCES

Leggett et al 2021 ApJ 918, 11

Marley et al. 2021 ApJ 920, 85 (and https://zenodo.org/record/5063476)

Meisner et al. 2023, ApJ in press 

Phillips et al. 2020 A & Ap 637, 38

Tremblin et al. 2015 ApJ 804, L17

Tremblin et al. 2016 ApJ 817, L19

Tremblin et al. 2019 ApJ 876, 144