J/A+A/703/A71 Stellar atmosphere opacity K broadened by H2 (Allard+, 2025)
Line shapes of the Na/K resonance line profiles perturbed by H2 at extreme
density.
Allard N.F., Kielkopf J.F.
<Astron. Astrophys. 703, A71 (2025)>
=2025A&A...703A..71A 2025A&A...703A..71A (SIMBAD/NED BibCode)
ADC_Keywords: Models ; Line Profiles
Keywords: lines: profiles - planets planets: atmospheres - brown dwarfs
Abstract:
Collision broadening by molecular hydrogen of sodium and potassium is
one of the major broadening mechanisms in the atmospheres of brown
dwarf stars and exoplanets at an effective temperature of about
1000K. The relevant H2 perturber densities reach several
1019cm-3 in hot (Teff≳1500K) Jupiter-mass planets, and up to
almost 1021cm-3 (∼30bar) for more massive or cooler objects. The
Juno Microwave Radiometer has enabled observations of Jupiter's
atmosphere down to previously inaccessible depths where pressures near
106bar have to be considered and the relevant H2 perturber
densities may exceed 1025cm-3.
While Na/K-He/H2 opacity tables have been constructed for the
resonance lines that are valid to nH2=1021cm-3, at higher
density it is important to ensure accurate absorption cross-sections
of these species in the models. We accurately determine the broadening
of Na/K by H2 in the unified theory at H2 densities larger than
1021cm-3 and compare to the corresponding Lorentzian profiles.
The theory of spectral line shapes, especially the unified approach we
have developed, makes possible accurate models of stellar spectra that
account both for the centers of spectral lines and their extreme wings
in one consistent treatment. In this study, we examine the density
dependence of the Na and K D2 (P3/2) components, respectively, at
5889.95Å and 7664.90Å from 1x1021 to 2x1022cm-3.
Lorentzian profiles from impact broadening theory are only valid in
the core of the line not farther than a few half-widths as long as
there is no overlap between the core of the line and possible
quasi-molecular features in the wings due to close collisions.
The accurate computation of line profiles from collision broadening
at high density requires use of a Fourier transform of the
autocorrelation function inside the model atmosphere code. We strongly
warn that use of Lorentzian profiles at a high perturber density
neglects radiation during close collisions and may lead to erroneous
conclusions.
Description:
Complete K-H2 opacity tables for the D1 and D2 components of the
resonance line.
README.pdf file for the description of the opacity tables and
explanations of their use, the files TABLESD1KH2_2015.tar.gz
and TABLESD2KH2_2015.tar.gz which contain the opacity tables
for the D1 and D2 components of the resonance line of K-H2.
A file EXAMPLEKH2820.tar.gz contains the results at T=820K,
and the programs to read the tables.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 512 . This file
README.pdf 512 127 ReadMe for the use of the tables
EXAMPLEKH2820.tar 1042 6116 Example with programs to read the tables
TABLESD1KH2_2015.tar 512 2220 K-H2 opacity tables for the D1 components
TABLESD2KH2_2015.tar 1069 3617 K-H2 opacity tables for the D2 components
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Acknowledgements:
Nicole Allerd, nicole.allard(at)obspm.fr
(End) Patricia Vannier [CDS] 23-Oct-2025