A New Equation of State for Dense Hydrogen–Helium Mixtures

Chabrier, G.; Mazevet, S.; Soubiran, François

doi:10.3847/1538-4357/aaf99f

Cited by 153 publications

(187 citation statements)

References 64 publications

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“…These changes are brought about by two major modelling improvements. First, the use of a new hydrogen and helium EOS (Chabrier et al 2019) in the interior structure model has raised the hydrogen and deuterium minimum masses, causing changes in the cooling tracks around these masses ( Figure 5). This new EOS includes quantum molecular dynamics calculations and predicts cooler, denser, and hence more degenerate objects than the previous semi-analytic EOS of Saumon et al (1995) used in previous works ( Figure 6).…”

Section: Evolutionary Tracksmentioning

confidence: 99%

“…We include updated line lists for important molecular absorbers and improved line shapes for the collisionally broadened potassium resonance lines. Finally, we couple these atmosphere models to an interior structure model which uses a new H-He EOS from Chabrier et al (2019) including ab initio quantum molecular dynamics calculations.…”

Section: Introductionmentioning

confidence: 99%

“…Interior temperature(top) and density (bottom) as a function of normalised radial mass profile of the simulated object. Solid blue lines are generated using the new EOS ofChabrier et al (2019), and the dashed orange lines are generated using the older EOS ofSaumon et al (1995).…”

mentioning

confidence: 99%

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A new set of atmosphere and evolution models for cool T–Y brown dwarfs and giant exoplanets

Phillips

Tremblin

Baraffe

et al. 2020

A&A

Self Cite

196

262

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We present a new set of solar metallicity atmosphere and evolutionary models for very cool brown dwarfs and self-luminous giant exoplanets, which we term ATMO 2020. Atmosphere models are generated with our state-of-the-art 1D radiative-convective equilibrium code ATMO, and are used as surface boundary conditions to calculate the interior structure and evolution of 0.001 − 0.075 M objects. Our models include several key improvements to the input physics used in previous models available in the literature. Most notably, the use of a new H-He equation of state including ab initio quantum molecular dynamics calculations has raised the mass by ∼ 1 − 2% at the stellar-substellar boundary and has altered the cooling tracks around the hydrogen and deuterium burning minimum masses. A second key improvement concerns updated molecular opacities in our atmosphere model ATMO, which now contains significantly more line transitions required to accurately capture the opacity in these hot atmospheres. This leads to warmer atmospheric temperature structures, further changing the cooling curves and predicted emission spectra of substellar objects. We present significant improvement for the treatment of the collisionally broadened potassium resonance doublet, and highlight the importance of these lines in shaping the red-optical and near-infrared spectrum of brown dwarfs. We generate three different grids of model simulations, one using equilibrium chemistry and two using non-equilibrium chemistry due to vertical mixing, all three computed self-consistently with the pressure-temperature structure of the atmosphere. We show the impact of vertical mixing on emission spectra and in colourmagnitude diagrams, highlighting how the 3.5 − 5.5 µm flux window can be used to calibrate vertical mixing in cool T-Y spectral type objects.

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Section: Evolutionary Tracksmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A new set of atmosphere and evolution models for cool T–Y brown dwarfs and giant exoplanets

Phillips

Tremblin

Baraffe

et al. 2020

A&A

Self Cite

196

262

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“…For the H 2 O layer we use the temperature-dependent H 2 O EOS compiled by Thomas & Madhusudhan (2016) Seager et al (2007) and Wagner & Pruß (2002). For the gaseous envelope we use the latest H/He EOS from Chabrier et al (2019) for a solar helium mass fraction (Y = 0.275).…”

Section: Internal Structure Modelmentioning

confidence: 99%

“…We explore a range of P -T profiles and choose two representative cases, with different T int , discussed further in sections 3.2 and 3.3. Where required by the internal structure model, the bottom of the P -T profile of the H/He envelope is continued to deeper pressures using the adiabatic gradient from Chabrier et al (2019). We also employ an adiabatic temperature profile in the H 2 O layer, following Thomas & Madhusudhan (2016).…”

Section: Internal Structure Modelmentioning

confidence: 99%

The Interior and Atmosphere of the Habitable-zone Exoplanet K2-18b

Madhusudhan

Nixon²,

Welbanks³

et al. 2020

ApJL

103

174

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Exoplanets orbiting M dwarfs present a valuable opportunity for their detection and atmospheric characterisation. This is evident from recent inferences of H 2 O in such atmospheres, including that of the habitable-zone exoplanet K2-18b. With a bulk density between Earth and Neptune, K2-18b may be expected to possess a H/He envelope. However, the extent of such an envelope and the thermodynamic conditions of the interior remain unexplored. In the present work, we investigate the atmospheric and interior properties of K2-18b based on its bulk properties and its atmospheric transmission spectrum. We constrain the atmosphere to be H 2 -rich with a H 2 O volume mixing ratio of 0.02 − 14.8%, consistent with previous studies, and find a depletion of CH 4 and NH 3 , indicating chemical disequilibrium. We do not conclusively detect clouds/hazes in the observable atmosphere. We use the bulk parameters and retrieved atmospheric properties to constrain the internal structure and thermodynamic conditions in the planet. The constraints on the interior allow multiple scenarios between rocky worlds with massive H/He envelopes and water worlds with thin envelopes. We constrain the mass fraction of the H/He envelope to be 6%; spanning 10 −5 for a predominantly water world to ∼ 6% for a pure iron interior. The thermodynamic conditions at the surface of the H 2 O layer range from the super-critical to liquid phases, with a range of solutions allowing for habitable conditions on K2-18b. Our results demonstrate that the potential for habitable conditions is not necessarily restricted to Earth-like rocky exoplanets.

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HST astrometry of the closest brown dwarfs‐II. Improved parameters and constraints on a third body

Bedin,

Dietrich,

Burgasser

et al. 2024

Astron Nachr

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Located at less than two pc away, Luhman 16 AB (WISE J104915.57‐531906.1) is the closest pair of brown dwarfs and the third closest “stellar” system to Earth. An exoplanet candidate in the Luhman 16 binary system was reported in 2017 based on a weak astrometric signature in the analysis of 12 HST epochs. An additional epoch collected in 2018 and re‐analysis of the data with more advanced methods further increased the significance level of the candidate, consistent with a Neptune‐mass exoplanet orbiting one of the Luhman 16 brown dwarf components. We report the joint analysis of these previous data together with two new astrometric HST epochs we obtained to confirm or disprove this astrometric signature. Our new analysis rules out the presence of a planet orbiting one component of the Luhman 16 AB system for masses 1.5 M♆ (Neptune masses) and periods between 400 and 5000 days. However, the presence of third bodies with masses 3 M♆ and periods between 2 and 400 days (1.1 years) cannot be excluded. Our measurements make significant improvements to the characterization of this sub‐stellar binary, including its mass‐ratio 0.8305 , individual component masses 35.40.2 MꝜ and 29.40.2 MꝜ (Jupiter masses), and parallax distance 1.9960 pc 50 AU. Comparison of the masses and luminosities of Luhman 16 AB to several evolutionary models shows persistent discrepancies in the ages of the two components, but strengthens the case that this system is a member of the 51095 Myr Oceanus Moving Group.

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A New Equation of State for Dense Hydrogen–Helium Mixtures

Cited by 153 publications

References 64 publications

A new set of atmosphere and evolution models for cool T–Y brown dwarfs and giant exoplanets

A new set of atmosphere and evolution models for cool T–Y brown dwarfs and giant exoplanets

The Interior and Atmosphere of the Habitable-zone Exoplanet K2-18b

HST astrometry of the closest brown dwarfs‐II. Improved parameters and constraints on a third body

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