2015/03/18 by Kevin Heng, Aurélien Wyttenbach, A. Wyttenbach +7 · 43 citations
Chemistry · Mathematics · Physics and Astronomy · #Absorption (acoustics) #Absorption spectroscopy #Astronomy and Astrophysical Research #Astrophysics #Astrophysics and Star Formation Studies #Chemistry #Computational physics #Emission spectrum #Exoplanet #Geometry #Isothermal process #Line (geometry) #Mathematics #Optics #Physics #Quantum mechanics #RADIUS #Spectral line #Stars #Stellar, planetary, and galactic studies #Thermodynamics #Transit (satellite) #astro-ph.EP #physics.ao-ph
paper · pdf · doi:10.1088/2041-8205/803/1/l9
published in The Astrophysical Journal Letters 803(1), L9 (IOP Publishing) · Accepted by ApJ Letters. 6 pages, 3 figures
arxiv created 2015/03/18 · openalex publication_date 2015/04/08 · arxiv updated 2015/06/24 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We present a theory for interpreting the sodium lines detected in transmission spectra of exoplanetary atmospheres. Previous analyses employed the isothermal approximation and dealt only with the transit radius. By recognizing the absorption depth and the transit radius as being independent observables, we develop a theory for jointly interpreting both quantities, which allows us to infer the temperatures and number densities associated with the sodium lines. We are able to treat a non-isothermal situation with a constant temperature gradient. Our novel diagnostics take the form of simple-to-use algebraic formulae and require measurements of the transit radii (and their corresponding absorption depths) at line center and in the line wing for both sodium lines. We apply our diagnostics to the HARPS data of HD 189733b, confirm the upper atmospheric heating reported by Huitson et al., derive a temperature gradient of 0.4376 ± 0.0154 K km −1 , and find densities ∼1–10 4 cm −3 .