The 2020 release of the ExoMol database: molecular line lists for exoplanet and other hot atmospheres (2007.13022v1)

Abstract: The ExoMol database (www.exomol.com) provides molecular data for spectroscopic studies of hot atmospheres. While the data is intended for studies of exoplanets and other astronomical bodies, the dataset is widely applicable. The basic form of the database is extensive line lists; these are supplemented with partition functions, state lifetimes, cooling functions, Land\'e g-factors, temperature-dependent cross sections, opacities, pressure broadening parameters, $k$-coefficients and dipoles. This paper presents the latest release of the database which has been expanded to consider 80 molecules and 190 isotopologues totaling over 700 billion transitions. While the spectroscopic data is concentrated at infrared and visible wavelengths, ultraviolet transitions are being increasingly considered in response to requests from observers. The core of the database comes from the ExoMol project which primarily uses theoretical methods, albeit usually fine-tuned to reproduce laboratory spectra, to generate very extensive line lists for studies of hot bodies. The data has recently been supplemented by line lists deriving from direct laboratory observations, albeit usually with the use of ab initio transition intensities. A major push in the new release is towards accurate characterisation of transition frequencies for use in high resolution studies of exoplanets and other bodies.

• The paper presents an expanded ExoMol database offering over 700 billion molecular transitions with accuracy from high-level quantum calculations and empirical data.
• It integrates with radiative transfer codes such as Tau-REx and NEMESIS, enabling precise modeling of diverse exoplanetary and astrophysical environments.
• Future enhancements will improve spectral coverage, pressure broadening, and temperature-dependent rates, further advancing molecular spectroscopy research.

Overview of the ExoMol Database: Molecular Line Lists for Exoplanet and Other Hot Atmospheres

The 2020 release of the ExoMol database represents a significant advancement in the provision of molecular data necessary for spectroscopic studies of hot planetary atmospheres, including exoplanets. This comprehensive resource aims to support both theoretical and practical research in astrophysics by offering an extensive catalog of molecular line lists, alongside auxiliary data such as partition functions, state lifetimes, and pressure broadening parameters.

Data Coverage and Methodology

ExoMol database has expanded its scope to include 80 molecules and 190 isotopologues, culminating in over 700 billion transitions. This expansion is driven by multiple scientific needs: understanding the atmospheres of newly discovered exoplanets, which feature diverse chemical compositions, and accommodating high-temperature environments like those observed in cool stars and brown dwarfs.

A cornerstone of this database is the use of high-level quantum mechanical calculations complemented by empirical measurements to enhance data accuracy. This dual approach ensures that the line lists produced are both extensive and reliable across the infrared and visible spectral regions, with efforts to extend into the ultraviolet spectrum in response to observational demands. The core theoretical tools used include variational programs and the MARVEL method for collating experimental energy levels, which provide critical high-resolution data necessary for the interpretation of Doppler-shift spectroscopy used in exoplanetary studies.

Major Contributions

ExoMol's contributions to the field are not limited to raw data. The database is heavily integrated into numerous radiative transfer and retrieval codes such as Tau-REx, NEMESIS, and ARCiS, providing essential input for modeling and analysis tools. These integrations extend ExoMol's utility beyond academic research, playing a pivotal role in planning future space missions like Ariel and JWST, where accurate molecular data is crucial for the successful interpretation of atmospheric spectra.

Key Developments and Applications

• Exoplanetary Atmospheres: The ExoMol database supports the detection and characterization of exoplanetary atmospheres, distinguishing molecular compositions in conditions ranging from cool gaseous giants to the extreme heat of lava planets. The database's ability to represent transitions at high resolution enables it to keep pace with advancements in observational techniques.
• Astrophysical Environments: Besides exoplanets, ExoMol serves applications related to cool stars, brown dwarfs, and even phenomena on Earth such as combustion processes and industrial emissions.
• MOLECULAR MODELLING: New advancements include the development of line lists for species like HCN, CH$_4$, H$_2$O, and others, which are critical for modeling the atmospheres of both terrestrial and gas giant exoplanets.

Future Prospects

Future developments of the ExoMol database will focus on increasing the accuracy of transition frequencies and exploring possible extensions into high-energy spectral regions. Enhancements in pressure broadening parameterization and the inclusion of temperature-dependent photodissociation rates are also anticipated. As the needs of astrophysical research evolve, ExoMol is poised to adapt, solidifying its role as a linchpin resource for spectroscopic analysis and astronomical exploration.

The ExoMol database stands as a vital tool in modern astrophysics, continuously updated to reflect the latest in molecular spectroscopy research. Its comprehensive approach and integration into key computational tools underscore its importance to both current research and the future exploration of the universe.