VUV-absorption cross section of carbon dioxide from 150 to 800 K and applications to warm exoplanetary atmospheres

Olivia Venot; Yves Bénilan; Nicolas Fray; Marie-Claire Gazeau; Franck Lefèvre; Et-touhami Es-sebbar; Eric Hébrard; Martin Schwell; Chiheb Bahrini; Franck Montmessin; Maxence Lefèvre; Ingo P. Waldmann

doi:10.1051/0004-6361/201731295

paper

VUV-absorption cross section of carbon dioxide from 150 to 800 K and applications to warm exoplanetary atmospheres

arXiv:1709.08415 · doi:10.1051/0004-6361/201731295

Abstract

Most exoplanets detected so far have atmospheric T significantly higher than 300K. Often close to their star, they receive an intense UV photons flux that triggers important photodissociation processes. The T dependency of VUV absorption cross sections are poorly known, leading to an undefined uncertainty in atmospheric models. Similarly, data measured at low T similar to that of the high atmosphere of Mars, Venus, and Titan are often lacking. Our aim is to quantify the T dependency of the abs. cross section of important molecules in planetary atmospheres. We want to provide both high-resolution data at T prevailing in these media and a simple parameterization of the absorption in order to simplify its use in photochemical models. This study focuses on carbon dioxide. We performed experimental measurements of CO $_{2}$ absorption cross section with synchrotron radiation for the wavelength range (115--200nm). For longer wavelengths (195--230nm), we used a deuterium lamp and a 1.5m Jobin-Yvon spectrometer. We used these data in our 1D thermo-photochemical model in order to study their impact on the predicted atmospheric compositions. The cross section of CO $_{2}$ increases with T. It can be separated in two parts: a continuum and a fine structure superimposed on the continuum. The variation of the continuum of absorption can be represented by the sum of three gaussian functions. Using data at high T in thermo-photochemical models modifies significantly the abundance and the photodissociation rates of many species, in addition to CO $_{2}$ , such as methane and ammonia. These deviations have an impact on synthetic transmission spectra, leading to variations of up to 5 ppm. We present a full set of HR ( $Δ λ$ =0.03nm) absorption cross sections of CO $_{2}$ from 115 to 230nm for T ranging from 150 to 800K.

14 pages, 17 figures, accepted for pulication in A&A

VUV-absorption cross section of carbon dioxide from 150 to 800 K and applications to warm exoplanetary atmospheres

Abstract

References in corpus (5)

Cited by in corpus (16)