Welcome to NEMESISPY’s documentation!

Table of Contents

• Usage
  • Installation
  • Data
  • Issues and contributions
• Tutorial
  • Hot Jupiter emission spectrum
• API
  • common
  • models
  • radtran
• Publications

Introduction

NEMESISPY is a Python package developed for atmospheric retrievals, which is the inference of atmospheric properties such as chemical abundances from observed spectra of planetary atmospheres. The workflow of atmospheric retrievals can be devided into two steps: forward modelling and model fitting:

• The forward modelling step requires an atmospheric model for the observed planet and a radiative transfer pipeline that can calculate model spectra given an atmospheric model.

• The model fitting step requires a parameter estimation code that can constrain the free parameters of the forward model by fitting the observed spectra.

NEMESISPY can perform both parametric atmospheric modelling and radiative transfer calculation for the retrievals of planetary spectra. It is a recent development of the well-established Fortran NEMESIS library, which has been applied to the atmospheric retrievals of both solar system planets and exoplanets. NEMESISPY can be easily interfaced with Bayesian inference algorithms such as nested sampling to retrieve atmospheric properties from spectroscopic observations. The radiative transfer calculations in NEMESISPY are done with the fast correlated-k method, and are accelerated with the Numba just-in-time compiler to match the speed of compiled languages such as Fortran. The radiative transfer routines are based on the well-tested NEMESIS library developed by Patrick Irwin (University of Oxford) and collaborators.

NEMESISPY comes ready with some spectral data and General Circulation Model (GCM) data so you can start simulating spectra immediately. There are a few demonstration routines in the nemesispy/examples folder; in particular, demo_fit_eclipse.py contains an interactive plot routine which allows you to fit a hot Jupiter eclipse spectrum by hand by varying its chemical abundance and temperature profile. The current release of NEMESISPY is focused on the calculation of thermal emission spectra of exoplanets. It is capale of calculating emission spectra at multiple orbital phases from an arbitray atmospheric model. Future releases will include more features such as multiple scattering and transmission geometry.

NEMESISPY has the following nice features:

• Written fully in Python (not a wrapper!): highly portable and customisable compared to packages written in compiled languages and can be easily installed on computer clusters.

• Fast calculation speed: the most time consuming routines are accelerated with just-in-time (JIT) compilation, which compiles Python code to machine code at run time.

• Radiative transfer routines are benchmarked against the extensively used NEMESIS library.

• Contains routines to simulate spectra from General Circulation Models (GCMs).

• Contains unit tests to check if the code is working correctly after modifications.

To install the package and keep it editable, clone the repository and type the following in the terminal:

$ pip install --editable .

To run all unit tests, change directory to the software folder and type the following in the terminal:

$ python -m unittest discover test/

Note

This project is under active development.

Contributors

NEMESISPY was originally developed by Jingxuan Yang (University of Oxford) and Dr Juan Alday (The Open University), with support from Prof. Patrick Irwin (University of Oxford). The project benefited from the numerous developers of the Fortran NEMESIS library, led and maintained by Prof. Patrick Irwin.

NEMESISPY is now under active development, with contributions from Agnibha Banerjee (The Open University), Dr Jo Barstow (The Open University), and Joseph Penn (University of Oxford).

The project is currently maintained by Jingxuan Yang. If you would like to contribute to the project, please contact the maintainer.

Citation

If you use NEMESISPY in your research, please cite the following paper:

• Jingxuan Yang, Patrick G J Irwin, Joanna K Barstow, Testing 2D temperature models in Bayesian retrievals of atmospheric properties from hot Jupiter phase curves, Monthly Notices of the Royal Astronomical Society, Volume 525, Issue 4, November 2023, Pages 5146–5167, https://doi.org/10.1093/mnras/stad2555,

as well as the original NEMESIS paper:

• P.G.J. Irwin, N.A. Teanby, R. de Kok, L.N. Fletcher, C.J.A. Howett, C.C.C. Tsang, C.F. Wilson, S.B. Calcutt, C.A. Nixon, P.D. Parrish, The NEMESIS planetary atmosphere radiative transfer and retrieval tool, Journal of Quantitative Spectroscopy and Radiative Transfer, Volume 109, Issue 6, 2008, Pages 1136-1150, ISSN 0022-4073, https://doi.org/10.1016/j.jqsrt.2007.11.006.