SIMBAD references

2019ApJ...881...25F - Astrophys. J., 881, 25-25 (2019/August-2)

How much information does the sodium doublet encode? Retrieval analysis of non-LTE sodium lines at low and high spectral resolutions.

FISHER C. and HENG K.

Abstract (from CDS):

Motivated by both ground- and space-based detections of the sodium doublet in the transmission spectra of exoplanetary atmospheres, we revisit the theory and interpretation of sodium lines in non-local thermodynamic equilibrium (NLTE), where collisions are not efficient enough to maintain a Boltzmann distribution for the excited and ground states of the sodium atom. We consider non-Boltzmann distributions that account for the ineffectiveness of collisions. We analyze the sodium doublet in transmission spectra measured at low (HAT-P-1b, HAT-P-12b, HD 189733b, WASP-6b, WASP-17b, and WASP-39b) and high (WASP-49b) spectral resolutions. Nested-sampling retrievals performed on low-resolution optical/visible transmission spectra are unable to break the normalization degeneracy if the spectral continuum is associated with Rayleigh scattering by small cloud particles. Using mock retrievals, we demonstrate that unnormalized ground-based, high-resolution spectra centered on the sodium doublet alone are unable to precisely inform us about the pressure levels probed by the transit chord and hence to identify the region (i.e., thermosphere, exosphere) of the atmosphere being probed. Retrievals performed on the HARPS transmission spectrum of WASP-49b support this conclusion. Generally, we are unable to distinguish between LTE versus NLTE interpretations of the sodium doublet based on the computed Bayesian evidence with the implication that LTE interpretations tend to underestimate the temperature probed by the transit chord. With the current low-resolution data, the sodium line shapes are consistent with Voigt profiles without the need for sub-Lorentzian wings. The retrieved sodium abundances are consistent with being subsolar to solar.

Abstract Copyright: © 2019. The American Astronomical Society. All rights reserved.

Journal keyword(s): planets and satellites: atmospheres

Simbad objects: 8

goto Full paper

goto View the reference in ADS

To bookmark this query, right click on this link: simbad:2019ApJ...881...25F and select 'bookmark this link' or equivalent in the popup menu


2021.04.17-11:08:35

© Université de Strasbourg/CNRS

    • Contact