PICASO 3.0 Atmospheric Models of WASP-39 b for the JWST Transiting Exoplanet Community Early Release Science Program

OVERVIEW

The exoplanetary atmospheric models used in the recent discovery of CO2  in WASP- 39 b's atmosphere by the JWST transiting exoplanet community early release science program are presented here. These models are also being used to analyze multiple observations of WASP 39-b obtained using various JWST instruments and observational modes by the transiting exoplanet ERS team. The 1D Radiative-Convective-Thermochemical Equilibrium (RCTE) atmospheric models were computed using the open-source 1D climate model PICASO 3.0 (Mukherjee et al. (2022)). These atmospheric models were then post-processed with condensation clouds using the open-source cloud model VIRGA (Rooney et al. (2022)). The atmospheric models were also post-processed with the 1D photochemical network code VULCAN (Tsai et al. (2021)) to explore photochemistry in WASP-39 b's atmosphere.

1D RCTE CLOUD-FREE MODELS

The base 1D RCTE grid includes atmospheric metallicity points at 0.1, 0.3, 1.0, 3.0, 10.0, 30.0, 50.0, and 100.0x solar values. The Carbon-to-Oxygen (C/O) ratio value is varied between four values - 0.23, 0.46, 0.69, and 0.92. The intrinsic temperature of the planet has been varied across 100, 200, and 300 K, whereas two values of the heat redistribution factor - 0.4 and 0.5 are included. A heat redistribution factor of 0.5 corresponds to the case of full heat redistribution. With these grid points, the grid includes a total of 8x4x3x2= 192 different models.

These models are in the "RCTE_cloud_free.zip" folder. The naming scheme of these files is "profile_eq_planet_[T_int]_grav_4.5_mh_[MH]_CO_[CtoO]_sm_0.0486_v_[rfacv]_.nc" where [T_int] represents the intrinsic temperature of the planet, [MH] is the log10 of the atmospheric metallicity relative to solar, [CtoO] is the C/O ratio relative to solar, and [rfacv] is the heat-redistribution factor. So, a metallicity value of 0.3xsolar will have a [MH] value of -0.5, and a C/O 0.46 is considered 1xsolar and will correspond to [CtoO]=1. [T_int] and [rfacv] can assume values described in the previous paragraph.

1D RCTE CLOUDY MODELS

The base 1D RCTE cloud-free models were post-processed to include condensation cloud species Na2S, MnS, and MgSiO3. The cloud structure and optical property calculations were performed using the VIRGA model where the sedimentation efficiency fsed and the vertical eddy diffusion coefficient (Kzz) are free parameters. For the cloudy models, 5  fsed  values - 0.6, 1, 3, 6, and 10 were used along with 3 different values of log10Kzz - 5, 7, 9, and 11, where Kzz is in cm2/s. These models are included in the "RCTE_cloudy.zip" folder following the naming structure "profile_eq_planet_[T_int]_grav_4.5_mh_[MH]_CO_[CtoO]_sm_0.0486_v_[rfacv]_kzz_1e[log10Kzz]_fsed_[fsed].cld.nc" where two other variables are added in the name - [log10Kzz] and [fsed]. Both of these variables can take values listed here.

PHOTOCHEMICAL CLOUD-FREE MODELS

A much smaller subset of the base 1D RCTE models were post-processed with the 1D photochemical network code VULCAN to simulate the effects of vertical mixing and photochemistry in WASP-39 b's atmosphere. log10Kzz  was varied again between the 5, 7, 9, and 11 for this purpose. These files are named as "profile_diseq_planet_[T_int]_grav_4.5_mh_[MH]_CO_[CtoO]_sm_0.0486_v_[rfacv]_kzz_1e[log10Kzz].nc" and can be found in the "photochem_cloud_free.zip" folder.

PHOTOCHEMICAL CLOUDY MODELS

The photochemical models were post-processed with clouds to simulate a cloudy atmosphere with disequilibrium chemistry. The fsed  and log10Kzz  grid system for the RCTE cloudy models has been used again for these models as well. These files are in the "photochem_cloudy.zip" folder and are named according to the format "profile_diseq_planet_[T_int]_grav_4.5_mh_[MH]_CO_[CtoO]_sm_0.0486_v_[rfacv]_kzz_1e[log10Kzz]_fsed_[fsed].cld.nc".

FILE FORMATTING AND USAGE

All the files are released in the xarray format. Each model has one single xarray file containing all metadata of that model. This metadata includes the input parameters used to compute the model, for example, the metallicity, C/O ratio, and intrinsic temperature. The temperature-pressure (T(P)) profile and the volume mixing ratio profiles of all the different gases in each model is also included in the metadata. The computed transmission spectrum of the model planet from 0.3-6 microns is included in the same file as well. The spectrum is calculated with resampled opacities at a spectral resolution of 60,000, but they should be re-binned at a spectral resolution of 3000 or less for comparison with observed data. For cloudy models, the wavelength dependant optical depth, asymmetry parameter, and single scattering albedo for each atmospheric layer are included in these xarray files.

We refer to this PICASO tutorial for reading/writing these xarray files. The spectrum from these xarray files can be easily extracted using the following code.

import xarray as xr

path = "path/to/files"
ds_sm = xr.open_dataset(path+"profile_eq_planet_300_grav_4.5_mh_+2.0_CO_2.0_sm_0.0486_v_0.5_.nc")

# for spectrum
wavelength = ds_sm['wavelength'].values
transit_depth = ds_sm['transit_depth'].values

# for T(P) profile
temperature = ds_sm['temperature'].values
pressure = ds_sm['pressure'].values

This tutorial shows how to use these models to analyze the NIRSpec Prism observations of WASP-39 b, which led to CO2 detection. Please note that the folders must be unzipped before using them with this notebook.

CREDITS

If you use these modeling products in your work, please cite this zenodo repository along with the following papers depending on the part of the grid being used:

1) RCTE_cloud_free.zip

 Mukherjee et al. (2022), Batalha et al. (2019) 

2) RCTE_cloudy.zip

Rooney et al. (2022), Mukherjee et al. (2022), Batalha et al. (2019) 

3) photochem_cloud_free.zip

 Tsai et al. (2021) , Mukherjee et al. (2022), Batalha et al. (2019) 

4) photochem_cloudy.zip

 Tsai et al. (2021) , Mukherjee et al. (2022), Batalha et al. (2019), Rooney et al. (2022)