Atomic and Molecular Opacities for Brown Dwarf and Giant Planet Atmospheres

By C. Sharp, Adam Burrows. 2006

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We present a comprehensive description of the theory and practice of opacity calculations from the infrared to the ultraviolet needed to generate models of the atmospheres of brown dwarfs and extrasolar giant planets. Methods for using existing line lists and spectroscopic databases in disparate formats are presented, and plots of the resulting absorptive opacities versus wavelength for the most important molecules and atoms at representative temperature/pressure points are provided. Electronic, rovibrational, bound-free, bound-bound, free-free, and collision-induced transitions and monochromatic opacities are derived, discussed, and analyzed. The species addressed include the alkali metals, iron, heavy metal oxides, metal hydrides, H2, H2O, CH4, CO, NH3, H2S, PH3, and representative grains. Once monochromatic absorption cross sections for all constituents have been derived, chemical abundances have to be obtained before the resulting product can be summed to obtain total opacities. Hence, we include a review of the thermochemistry, techniques, and databases needed to derive equilibrium abundances and provide some sample results.

Subfields: Atmospheric Science, Atomic and Molecular Physics, and Optics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/cfa0d9d26242cb4fa21622b16e5d350a47faf3a2

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Citations in the corpus

A variationally computed line list for hot NH3 (2010, background): “…whilst the spectra of M and L-type brown dwarfs are dominated by H2O, and CH4 becomes increasingly important at lower temperatures, NH3 is a significant source of opacity in the atmospheres of late T-type dwarfs, particularly in the 10.5 µm region (Burrows et al. 1997; Sharp & Burrows 2007).”
On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets (2014, background): “Thus, line shape profiles are commonly truncated at some distance from line center, which necessitates a re-scaling of the line shape to maintain the normalization of Equation 20, thus preserving the integrated line strength (Sharp & Burrows 2007).”
DETECTION OF H2O AND EVIDENCE FOR TiO/VO IN AN ULTRA-HOT EXOPLANET ATMOSPHERE (2016, background): “At temperatures above 2000 K, models predict that gaseous titanium oxide (TiO) and vanadium oxide (VO) are important absorbers, especially at optical wavelengths (e.g. Hubeny et al. 2003; Sharp & Burrows 2007; Fortney et al. 2008).”
CAN TiO EXPLAIN THERMAL INVERSIONS IN THE UPPER ATMOSPHERES OF IRRADIATED GIANT PLANETS? (2009, background): “Models of this planet with 40% solar TiO and with 100% solar TiO are presented, along with the corresponding condensation curves (Sharp & Burrows 2007).”
The Evolution of L and T Dwarfs in Color-Magnitude Diagrams (2008, background): “…number of gas and condensate species (Allard et al. 2001; Lodders 2002), increasingly complete molecular opacity databases (Freedman et al. 2008; Sharp & Burrows 2007), extreme resonance line broadening (Burrows et al. 2000; Allard et al. 2005), and particulate cloud models (Allard et al. 2001;…”
Synthetic Spectra and Colors of Young Giant Planet Atmospheres: Effects of Initial Conditions and Atmospheric Metallicity (2008, background): “We must also caution that although our understanding of the gaseous opacity in these atmospheres is improving (Sharp & Burrows 2007; Freedman et al. 2008), calculations of the contribution dueto CH4 are quite uncertain.”
DISEQUILIBRIUM CARBON, OXYGEN, AND NITROGEN CHEMISTRY IN THE ATMOSPHERES OF HD 189733b AND HD 209458b (2011, background): “Thermochemical equilibrium is assumed for most models (e.g., Burrows & Sharp 1999; Seager et al. 2000; Lodders & Fegley 2002; Sharp & Burrows 2007; Burrows et al. 2007, 2008; Fortney et al. 2008a; Visscher et al. 2010a), although potential departures from equilibrium are sometimes explored through…”
ExoMol: molecular line lists for exoplanet and other atmospheres (2012, unknown): “Table 3 has been constructed from the literature (eg Sharp & Burrows (2007); Freedman et al. (2008)) and as a result of extended discussions with several scientists involved directly or indirectly in characterising exoplanets.”
A Unified Theory for the Atmospheres of the Hot and Very Hot Jupiters: Two Classes of Irradiated Atmospheres (2007, background): “In the absence of this effect V would not condense until ∼200 K cooler temperatures are reached and solid VO forms, as in the chemistry calculations of Burrows & Sharp (1999), Allard et al. (2001), and Sharp & Burrows (2007).”
Re-analysis of ammonia spectra: Updating the HITRAN 14NH3 database (2013, background): “Ammonia is also known to be present in both gas giants [9] and cool brown dwarfs [10,11] where it provides an important source of opacity.”
Transmission spectral properties of clouds for hot Jupiter exoplanets (2014, background): “…+ bn) , (2) where σext and σscatt are the extinction and scattering crosssections respectively, a is the grain radius, x is the size parameter (x = 2πa/λ), and an and bn are the mix coefficients expressed in terms of the complex index of refraction (see Sharp & Burrows 2007 for full equations).”
THE 0.8–14.5 μm SPECTRA OF MID-L TO MID-T DWARFS: DIAGNOSTICS OF EFFECTIVE TEMPERATURE, GRAIN SEDIMENTATION, GAS TRANSPORT, AND SURFACE GRAVITY (2009, background): “…and C2H6; the atomic lines of alkali metals Li, Na, K, Rb, and Cs; continuum opacity from H2 collisioninduced absorption; Rayleigh scattering by H2, H, and He; bound-free opacity from H − and H+2 ; and free-free opacity from H −, He−, H−2 , and H + 2 (Sharp & Burrows 2007; Freedman et al. 2008).”
HST hot-Jupiter transmission spectral survey: evidence for aerosols and lack of TiO in the atmosphere of WASP-12b (2013, background): “Significant opacity by CrH can also be excluded, as abundances needed to match the WFC3 near-IR Rp/R∗ levels would produce strong features between 8000 and 10,000 Å which would rise to ∼0.122 Rp/R∗, where the opacity of CrH is strongest (Sharp & Burrows 2007), though no such features are apparent.”