Title:The Influence of Pressure Broadening on Exoplanet Atmosphere Spectra — Ehsan Gharib Nezhad
Research Assistant, Arizona State University —
Abstract: A key ingredient in inferring the abundances of particular molecules, hence the atmospheric composition of exoplanet atmospheres are the molecular absorption cross sections. It is well known that pressure broadening significantly influences the absorption cross sections of a given molecule. Laboratory spectroscopic studies have shown that the line-broadening (i.e. Doppler, Lorentzian) is influence by several factors including temperature, pressure, dipole moment of the broadeners (or bath gases). Since absorption cross-sections are central to both atmospheric modeling and observational research, there is a critical need to investigate the effect of pressure line-broadening on the absorption cross-sections and subsequent influence on observed transmission and emission spectra of transiting exoplanets. Typical data-model comparisons (either forward modeling or retrieval’s) generally rely upon pre-computed grids of absorption cross-sections that assume trace molecules are broadened by a solar composition mixture (e.g., mainly H2 and He as a bath gas). However, as the metallicity of a planetary atmosphere increases, as anticipated for smaller planets in the sub-Neptune-Super Earth range, broadening due to other gases (e.g., N2, CO2, H2O, CH4, CO) can become significant and the H2-He broadening is no longer appropriate. To this end, I will represent the consequence of disregarding self-broadening of H2O in modeling emission and transmission spectra of steam atmospheres.
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