HITEMP: High-temperature spectroscopic parameters for observations of stellar, brown-dwarf and planetary atmospheres

Spectroscopic databases are essential for the remote sensing of astronomical environments. In particular, high-resolution spectral observations of high-temperature atmospheres of exoplanets and brown dwarfs allow for detections of molecular species and resultant characterizations of these objects. Considering the available observing opportunities over the coming years (e.g., using JWST, VLT, Ariel), it is therefore imperative that the spectroscopic databases are not only complete, but provide accurate positions, intensities, and contain appropriate broadening parameters. It is also necessary to account for significantly more transitions when modeling radiative transfer of high-temperature atmospheres than would be required at terrestrial temperatures.

The HITEMP database [1], which provides line-by-line molecular spectroscopic parameters for use at high temperatures, was constructed to fulfill these requirements. HITEMP has been undergoing a significant upgrade that has improved the quality and extent of spectroscopic data. In addition, the number of line lists available has expanded, and now includes eight molecules: H₂O, CO₂, N₂O, CO, CH₄, NO, NO₂, OH [1-4]. Furthermore, for the line list for CH₄ [4] an intensity compression technique was implemented that facilitated HITEMP to be capable of accurately modeling high-temperature spectra of CH₄ up to 2000 K, while remaining practical to use. A summary of the latest updates to the HITEMP database will be presented, along with examples of validations that are a crucial component for the HITEMP/HITRAN project.

[1] Rothman, et al. (2010), JQSRT 111, 2139; [2] Hargreaves, et al. (2019), JQSRT 232, 35; [3] Li, et al. (2015), ApJS 216, 15; [4] Hargreaves, et al. (2020), ApJS 247, 55