Calculations of the Far-Wing Line Profiles of Sodium and Potassium in the Atmospheres of Substellar-Mass Objects

By Adam Burrows, M. Volobuyev. 2002

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At the low temperatures achieved in cool brown dwarf and hot giant planet atmospheres, the less refractory neutral alkali metals assume an uncharacteristically prominent role in spectrum formation. In particular, the wings of the Na-D (5890 Å) and K I (7700 Å) resonance lines come to define the continuum and dominate the spectrum of T dwarfs from 0.4 to 1.0 μm. Whereas in standard stellar atmospheres the strengths and shapes of the wings of atomic spectral lines are rarely needed beyond 25 Å from a line center, in brown dwarfs the far wings of the Na and K resonance lines out to thousands of angstroms detunings are important. Using standard quantum chemical codes and the unified Franck-Condon model for line profiles in the quasi-static limit, we calculate the interaction potentials and the wing line shapes for the dominant Na and K resonance lines in H2- and helium-rich atmospheres. Our theory has natural absorption profile cutoffs, has no free parameters, and is readily adapted to spectral synthesis calculations for stars, brown dwarfs, and planets with effective temperatures below 2000 K.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/c2cbe8a88891a63a16de925527e24c6156314a49

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Citations in the corpus

L and T Dwarf Models and the L to T Transition (2005, background): “The opacities of the alkali metal atoms are taken from Burrows, Marley, & Sharp (2000), which are similar in the line cores and near wings to those found in Burrows & Volobuyev (2003).”
Beyond the T Dwarfs: Theoretical Spectra, Colors, and Detectability of the Coolest Brown Dwarfs (2003, background): “The opacities of the alkali metal atoms are taken from Burrows, Marley, & Sharp (2000), which are similar in the line cores and near wings to those found in Burrows & Volobuyev (2003).”
Near-Infrared Photometry and Spectroscopy of L and T Dwarfs: The Effects of Temperature, Clouds, and Gravity (2004, background): “Since the Z band is sensitive to the far wings of the optical Na-D and K i resonance lines (Burrows & Volobuyev 2003) these variations might arise from differences in the removal of gaseous Na and K, due to gravity or metallicity effects.”
The Spectra of T Dwarfs. II. Red Optical Data (2003, background): “The peak-up in flux between these features is clearly evident, and their shapes are consistent with heavily pressure-broadened atomic lines (Burrows & Volobuyev 2003).”
Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e (2020, background): “Notable points of difference in the opacity treatment between Exo-REM and petitRADTRANS are the use of different alkali wing profiles (Burrows & Volobuyev 2003 for Exo-REM, Allard et al. 2003, 2012b for petitRADTRANS) and that petitRADTRANS assumed irragularly shaped, crystalline Fe and MgSiO3…”
FURTHER DEFINING SPECTRAL TYPE “Y” AND EXPLORING THE LOW-MASS END OF THE FIELD BROWN DWARF MASS FUNCTION (2012, background): “The resonance lines of Na I and K I fall at optical wavelengths, where cold brown dwarfs have little flux, but the broad wings of these lines extend very far from the line cores and are believed to have an influence on the emergent flux as longward as 1 µm (Burrows & Volobuyev 2003).”
New spectral types L and T (2005, background): “Burrows & Volobuyev (2003) studied the absorption cross-sections of H2-perturbed sodium and potassium atoms using quantum chemical codes and were able to model the red wing of the K I doublet (7665, 7699 Å) and the red wing of the Na I doublet (5890, 5896 Å).”
Line and Mean Opacities for Ultracool Dwarfs and Extrasolar Planets (2007, background): “Burrows & Volobuyev (2003) and Allard et al. (2003) have further modeled the pressure-broadened alkali lines.”
Hubble Space Telescope NICMOS Observations of T Dwarfs: Brown Dwarf Multiplicity and New Probes of the L/T Transition (2006, background): “With F110W-F170M = 2.31±0.14, this source is likely to be a highly reddened background star or faint unresolved galaxy. continuum suppressed by pressure-broadened Na I and K I lines (Burrows & Volobuyev 2003).”
YOUNG L DWARFS IDENTIFIED IN THE FIELD: A PRELIMINARY LOW-GRAVITY, OPTICAL SPECTRAL SEQUENCE FROM L0 TO L5 (2008, background): “However, condensates are not expected to significantly influence optical spectra due to the greater gas opacities in this region, in particular the pressure-broadened K I and Na I lines (Burrows & Volobuyev 2003).”