K–H<sub>2</sub>line shapes for the spectra of cool brown dwarfs

Allard, N. F.; Spiegelman, Fernand; Kielkopf, John F.

doi:10.1051/0004-6361/201628270

Cited by 124 publications

(87 citation statements)

References 30 publications

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“…These authors have recently developed a newer theory (Allard et al 2016), superseding their previous work, valid to higher densities. At 30 bar and 1900 K, the molecular hydrogen densities in the atmosphere of our companion are just above the upper limit of the previous Allard et al (2007b) theory and the strength of the broadened wing is uncertain, particularly in Y band.…”

Section: Benchmarkingcontrasting

confidence: 60%

COol Companions ON Ultrawide orbiTS (COCONUTS). I. A High-gravity T4 Benchmark around an Old White Dwarf and a Re-examination of the Surface-gravity Dependence of the L/T Transition

Zhang

Liu

Hermes

et al. 2020

ApJ

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We present the first discovery from the COol Companions ON Ultrawide orbiTS (COCONUTS) program, a large-scale survey for wide-orbit planetary and substellar companions. We have discovered a co-moving system COCONUTS-1, composed of a hydrogen-dominated white dwarf (PSO J058.9855 + 45.4184; d = 31.5 pc) and a T4 companion (PSO J058.9869 + 45.4296) at a 40.6 (1280 au) projected separation. We derive physical properties for COCONUTS-1B from (1) its near-infrared spectrum using cloudless Sonora atmospheric models, and (2) its luminosity and the white dwarf's age (7.3 +2.8 −1.6 Gyr) using Sonora evolutionary models. The two methods give consistent temperatures and radii, but atmospheric models infer a lower surface gravity and therefore an unphysically young age. Assuming evolutionary model parameters (T eff = 1255 +6 −8 K, log g = 5.44 +0.02 −0.03 dex, R = 0.789 +0.011 −0.005 R Jup ), we find cloudless model atmospheres have brighter Y -and J-band fluxes than the data, suggesting condensate clouds have not fully dispersed around 1300 K. The W2 flux (4.6 µm) of COCONUTS-1B is fainter than models, suggesting non-equilibrium mixing of CO. To investigate the gravity dependence of the L/T transition, we compile all 60 known L6−T6 benchmarks and derive a homogeneous set of temperatures, surface gravities, and masses. As is wellknown, young, low-gravity late-L dwarfs have significantly fainter, redder near-infrared photometry and ≈ 200 − 300 K cooler temperatures than old, high-gravity objects. Our sample now reveals such gravity dependence becomes weaker for T dwarfs, with young objects having comparable near-infrared photometry and ≈ 100 K cooler temperatures compared to old objects. Finally, we find that young objects have a larger amplitude J-band brightening than old objects, and also brighten at H band as they cross the L/T transition.

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Section: Benchmarkingcontrasting

confidence: 60%

COol Companions ON Ultrawide orbiTS (COCONUTS). I. A High-gravity T4 Benchmark around an Old White Dwarf and a Re-examination of the Surface-gravity Dependence of the L/T Transition

Zhang

Liu

Hermes

et al. 2020

ApJ

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“…In this work, the pressure-and temperature-broadened profiles for the resonance doublets of Na and K are computed using Allard et al (2016) and Allard et al (2019). Future updates to these opacities intend to also consider He broadening, as outlined in Peach et al (2020).…”

Section: Atomic Na and K Broadeningmentioning

confidence: 99%

“…(1i) The energy states from Engel et al (2005) are used in the Amaral et al (2019) line list for HeH + . (1j) The pressure and temperature broadened profiles for the resonance doublets of Na and K are computed using Allard et al (2016) and Allard et al (2019). See section 3.2.3 for a discussion on the broadening profiles of these atoms.…”

Section: Comments On Individual Speciesmentioning

confidence: 99%

The ExoMolOP database: Cross sections andk-tables for molecules of interest in high-temperature exoplanet atmospheres

Chubb

Rocchetto

Yurchenko

et al. 2021

A&A

134

116

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Here we present a publicly available database of opacities for molecules of astrophysical interest named ExoMolOP that has been compiled for over 80 species, and is based on the latest line list data from the ExoMol, HITEMP, and MoLLIST databases. These data are generally suitable for characterising high-temperature exoplanet or cool stellar and substellar atmospheres, and have been computed at a variety of pressures and temperatures, with a few molecules included at room temperature only from the HITRAN database. The data are formatted in different ways for four different exoplanet atmosphere retrieval codes; ARCiS, TauREx, NEMESIS, and petitRADTRANS, and include both cross sections (at R = λ ∆λ = 15,000) and k-tables (at R = λ ∆λ = 1000) for the 0.3-50µm wavelength region. Opacity files can be downloaded and used directly for these codes. Atomic data for alkali metals Na and K are also included, using data from the NIST database and the latest line shapes for the resonance lines. Broadening parameters have been taken from the literature where available, or have been estimated from the parameters of a known molecule with similar molecular properties where no broadening data are available. The data are available from www.exomol.com.

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“…Finally, we find some inconsistencies between predicted and retrieved alkali abundances. This could be due to the difficulties in determining an appropriate description for the pressure-broadened wings of the alkali lines (Sharp & Burrows 2007;Allard et al 2016) and/or the details of condensate rainout chemistry (which our model does not account for). Furthermore, brown dwarf abundance determinations typically assume that elemental metal ratios are solar, i.e., if we increase the metallicity, all metal abundances increase by that same factor.…”

Section: Comparison To Equilibrium Chemistry Predictionsmentioning

confidence: 99%

Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs. II. Properties of 11 T dwarfs

Line

Marley

Liu

et al. 2017

ApJ

104

155

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Brown dwarf spectra are rich in information revealing of the chemical and physical processes operating in their atmospheres. We apply a recently developed atmospheric retrieval tool to an ensemble of late-T dwarf (600-800 K) near-infrared (1-2.5 μm) spectra. With these spectra we are able to directly constrain the molecular abundances for the first time of H 2 O, CH 4 , CO, CO 2 , NH 3 , H 2 S, and Na+K, surface gravity, effective temperature, thermal structure, photometric radius, and cloud optical depths. We find that ammonia, water, methane, and the alkali metals are present and that their abundances are well constrained in all 11 objects. We find no significant trend in the water, methane, or ammonia abundances with temperature, but find a very strong (>25σ) decreasing trend in the alkali metal abundances with decreasing effective temperature, indicative of alkali rainout. As expected from previous work, we also find little evidence for optically thick clouds. With the methane and water abundances, we derive the intrinsic atmospheric metallicity and carbon-to-oxygen ratios. We find in our sample that metallicities are typically subsolar (−0.4 < [M/H] < 0.1 dex) and carbon-to-oxygen ratios are somewhat supersolar (0.4 < C/O < 1.2), different than expectations from the local stellar population. We also find that the retrieved vertical thermal profiles are consistent with radiative equilibrium over the photospheric regions. Finally, we find that our retrieved effective temperatures are lower than previous inferences for some objects and that some of our radii are larger than expectations from evolutionary models, possibly indicative of unresolved binaries. This investigation and method represent a new and powerful paradigm for using spectra to determine the fundamental chemical and physical processes governing cool brown dwarf atmospheres.

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K–H₂line shapes for the spectra of cool brown dwarfs

Cited by 124 publications

References 30 publications

COol Companions ON Ultrawide orbiTS (COCONUTS). I. A High-gravity T4 Benchmark around an Old White Dwarf and a Re-examination of the Surface-gravity Dependence of the L/T Transition

COol Companions ON Ultrawide orbiTS (COCONUTS). I. A High-gravity T4 Benchmark around an Old White Dwarf and a Re-examination of the Surface-gravity Dependence of the L/T Transition

The ExoMolOP database: Cross sections andk-tables for molecules of interest in high-temperature exoplanet atmospheres

Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs. II. Properties of 11 T dwarfs

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K–H2line shapes for the spectra of cool brown dwarfs

Cited by 124 publications

References 30 publications

COol Companions ON Ultrawide orbiTS (COCONUTS). I. A High-gravity T4 Benchmark around an Old White Dwarf and a Re-examination of the Surface-gravity Dependence of the L/T Transition

COol Companions ON Ultrawide orbiTS (COCONUTS). I. A High-gravity T4 Benchmark around an Old White Dwarf and a Re-examination of the Surface-gravity Dependence of the L/T Transition

The ExoMolOP database: Cross sections andk-tables for molecules of interest in high-temperature exoplanet atmospheres

Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs. II. Properties of 11 T dwarfs

Contact Info

Product

Resources

About

K–H₂line shapes for the spectra of cool brown dwarfs