Some objects and phenomena in the Universe can only be properly studied from space. For instance because they mainly emit radiation that is blocked by the Earth’s atmosphere, such as X-rays or infrared light. Weak light sources such as exoplanets are also best observed with space telescopes, because those are unhindered by light pollution and vibrations in the air.
Astrophysics
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Low energy
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High energy
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Exoplanets
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Software Packages
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ARCiS
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RADEX
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SPEX
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Publications
Software Packages
To get the best scientific results from the measurement data of our instruments, we develop our own software. With those programmes, we can calculate what spectrum we expect to see for an object and compare it with the real measurement. We make this software available to everyone.
ARCiS
ARCiS is a novel code for the analysis of exoplanet transmission and emission spectra. The aim of the modelling framework is to provide a tool able to link observations to physical models of exoplanet atmospheres. The software is constantly being improved and has been used during the analysis of cutting-edge data from current facilities such as HST and JWST. It will also be used for fitting the data from the upcoming ESA Ariel mission.
Download and install
The easiest way to download and install ARCiS is via GitHub, click here
Help and documentation
The User guide is available at this link.
More information, including data downloads, can be found here.
RADEX
RADEX is a software package to calculate the strengths of molecular and atomic lines from homogeneous gas clouds in the infra-red and microwave band. The user can select a certain molecule and set the temperature, density, column density and line width. Based on these parameters, the program then calculates the position and strength of the emission lines. The program can be run through a web interface or offline on a Linux or Mac computer.
Download and install
The software, written in Fortran, is available for download.
The website also includes installation instructions assuming you have a Fortran compiler installed.
Information and help
The RADEX website also contains information about how to run the program. More information about the calculations can be found on Zenodo.
Questions or bug reports can be submitted as an issue to our Github issue tracker.
The source code of RADEX is available on Github and Zenodo under an Apache 2.0 license. Everyone is free to use the program. We do request that authors who make use of the RADEX program cite our paper: Van der Tak, F.F.S., et al. 2007 .
SPEX
SPEX is an X-ray spectral analysis software package optimized for the interpretation of high-resolution astrophysical X-ray spectra. The software is especially suited for fitting spectra obtained by current X-ray observatories like XMM-Newton, Chandra, Suzaku, and XRISM. SPEX will be continuously improved to handle spectra from high-resolution X-ray instruments on future missions like NewAthena.
SPEX is open source software and is distributed with a GPLv3 license. The source code is available on Zenodo.
Download and install
SPEX is developed for Linux and Mac systems, but can also run on the Windows subsystem for Linux (WSL) or using a virtual machine. More information about downloading and installing SPEX can be found using this link.
Help and documentation
The SPEX documentation is available on Github. For questions and bug reports, users can submit an issue to the Github repository.
Pyspextools
In addition to the SPEX package, we also have a Python package called pyspextools. This contains tools to convert between files in OGIP format and SPEX format. More information about Pyspextools can be found here:
The pyspextools package is distributed with the Apache 2.0 license.
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Gas rotation and turbulence in the galaxy cluster Abell 2029
01/05/2026 - High-Energy
Aims. We constrain the rotation and turbulent support of the intracluster medium (ICM) in Abell 2029 (A2029) using dynamical equilibrium models and a combination of state-of-the-art X-ray and microwave datasets. Methods. The rotating turbulent ICM in the model has a composite polytropic distribution in equilibrium in a spherically symmetric, cosmologically motivated dark halo. The profile…
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Silicon, Sulfur, and Iron in the Interstellar Medium: A High-resolution X-Ray Spectral Study of GX 340+0
01/05/2026 - High-Energy
High-resolution X-ray spectroscopy provides a powerful probe of the interstellar medium (ISM), giving direct access to the composition and physical state of dust grains and atomic species in dense environments. We present a study of the gas and dust along the line of sight to the bright low-mass X-ray binary GX 340+00, which samples higher-density…
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Silicon-based vacuum window for millimeter- and submillimeter-wave astrophysics
01/05/2026 - Technology
We designed, fabricated, and characterized the properties of a silicon-based vacuum window suitable for millimeter-wave astrophysical applications. The window, which has a diameter of 124 mm, an optically usable diameter of 68 mm, and a thickness of about 4 mm, gives an average transmittance and reflectance of 99.6±3.5% and 1.3±1.4%, respectively, a fractional bandwidth of…
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Our experts
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Read moreTerri Brandt
Head of Astrophysics Programme (Dr.)