Non-equilibrium Chemistry in the Atmospheres of Brown Dwarfs

Saumon, D.; Marley, Mark S.; Lodders, K.; Freedman, Richard

doi:10.1017/s0074180900210899

Cited by 53 publications

(54 citation statements)

References 20 publications

(37 reference statements)

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“…This same effect has now been observed in brown dwarf Mband photometry (Golimowski et al, 2004), as anticipated by Fegley & Lodders (1996). This excess CO leads to strong absorption at 4.5 µm, leading to diminished flux in M-band (Saumon et al, 2003). Consequently, when searching for giant planets, L-band may be just as favorable as M-band.…”

Section: Other Detectability Issuessupporting

confidence: 75%

See 1 more Smart Citation

Young Jupiters are faint: new models of the early evolution of giant planets

Fortney¹,

Marley

Hubickyj

et al. 2005

Astron Nachr

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Abstract.Here we show preliminary calculations of the cooling and contraction of a 2 MJ planet. These calculations, which are being extended to 1-10 MJ, differ from other published "cooling tracks" in that they include a core accretion-gas capture formation scenario, the leading theory for the formation of gas giant planets. We find that the initial post-accretionary intrinsic luminosity of the planet is ∼3 times less than previously published models which use arbitrary initial conditions. These differences last a few tens of millions of years. Young giant planets are intrinsically fainter than has been previously appreciated. We also discuss how uncertainties in atmospheric chemistry and the duration of the formation time of giant planets lead to challenges in deriving planetary physical properties from comparison with tabulated model values.

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Section: Other Detectability Issuessupporting

confidence: 75%

“…We use the elemental abundance data of Lodders (2003) and compute chemical equilibrium compositions following Fegley & Lodders (1994) and Lodders & Fegley (2002). In addition, we maintain a large and constantly updated opacity database.…”

Section: Atmosphere Modelsmentioning

confidence: 99%

Young Jupiters are faint: new models of the early evolution of giant planets

Fortney¹,

Marley

Hubickyj

et al. 2005

Astron Nachr

Self Cite

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“…The lithium abundance has been reduced by a factor 1000 in the T eff = 1300 K model in order to provide a meaningful upper limit to the observed levels of Li i absorption in the spectrum of ε Indi Ba. Griffith & Yelle (1999) and Saumon et al (2003) have shown that this excess can be explained by the upmixing of CO from the warm deeper layers, since if one assumes sufficiently efficient turbulent mixing in the upper atmosphere, the kinetic rates for the conversion reactions from CO to CH 4 are too slow to adjust the mixing ratios to CE abundances. The BT-Settl models employ a similar calculation of these CE departure effects, but using diffusion coefficients derived from the CO5BOLD radiation hydrodynamics simulations (Freytag et al 2010) rather than adjusting them as a free parameter (Homeier et al, in prep.).…”

Section: Chemical Equilibrium Departuresmentioning

confidence: 99%

“…between 1000 and 1500 K, the diffusion coefficient in this part of the overshoot region would best characterise our model, corresponding to 10 7 −10 8 cm 2 /s in the ε Indi Ba model. In addition, we consider several reaction pathways and timescales besides the one from Prinn & Barshay (1977), on which the Saumon et al (2003) models are based, notably the revised time scale for the scheme of Prinn & Barshay (1977) suggested by Griffith & Yelle (1999), and the reaction scheme of Yung et al (1988) (see also Griffith & Yelle 1999). Among these, the Yung et al (1988) model generally predicts the fastest conversion rates from CO to CH 4 , and the Prinn & Barshay (1977) model with the modified rates of Griffith & Yelle (1999) the slowest rates, implying the strongest CE departure effects.…”

Section: Chemical Equilibrium Departuresmentioning

confidence: 99%

$\mathsf{\varepsilon}$ Indi Ba, Bb: a detailed study of the nearest known brown dwarfs

King¹,

McCaughrean

Homeier

et al. 2010

A&A

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The discovery of ε Indi Ba, Bb, a binary brown dwarf system very close to the Sun, makes possible a concerted campaign to characterise the physical parameters of two T dwarfs. Recent observations suggest substellar atmospheric and evolutionary models may be inconsistent with observations, but there have been few conclusive tests to date. We therefore aim to characterise these benchmark brown dwarfs to place constraints on such models. We have obtained high angular resolution optical, near-infrared, and thermal-infrared imaging and medium-resolution (up to R ∼ 5000) spectroscopy of ε Indi Ba, Bb with the ESO VLT and present VRIzJHKL M broad-band photometry and 0.63−5.1 μm spectroscopy of the individual components. The photometry and spectroscopy of the two partially blended sources were extracted with a custom algorithm. Furthermore, we use deep AO-imaging to place upper limits on the (model-dependent) mass of any further system members. We derive luminosities of log L/L = −4.699 ± 0.017 and −5.232 ± 0.020 for ε Indi Ba, Bb, respectively, and using the dynamical system mass and COND03 evolutionary models predict a system age of 3.7−4.3 Gyr, in excess of previous estimates and recent predictions from observations of these brown dwarfs. Moreover, the effective temperatures of 1352−1385 K and 976−1011 K predicted from the COND03 evolutionary models, for ε Indi Ba and Bb respectively, are in disagreement with those derived from the comparison of our data with the BT-Settl atmospheric models where we find effective temperatures of 1300−1340 K and 880−940 K, for ε Indi Ba and Bb respectively, with surface gravities of log g = 5.25 and 5.50. Finally, we show that spectroscopically determined effective temperatures and surface gravities for ultra-cool dwarfs can lead to underestimated masses even where precise luminosity constraints are available.

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“…A non-equilibrium correction to the equilibrium abundances of CH 4 /CO and NH 3 /N 2 due to vertical mixing (Saumon et al 2003) has been adopted to explain the observations of these species in brown dwarfs. A similar nonequilibrium treatement is used by Barman et al (2011a) to model the exoplanet HR8799b.…”

Section: Departures From Equilibriummentioning

confidence: 99%

The Dawes Review 3: The Atmospheres of Extrasolar Planets and Brown Dwarfs

Bailey

2014

Publ. Astron. Soc. Aust.

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The last few years has seen a dramatic increase in the number of exoplanets known and in the range of methods for characterising their atmospheric properties. At the same time, new discoveries of increasingly cooler brown dwarfs have pushed down their temperature range which now extends down to Y-dwarfs of < 300 K. Modelling of these atmospheres has required the development of new techniques to deal with the molecular chemistry and clouds in these objects. The atmospheres of brown dwarfs are relatively well understood, but some problems remain, in particular the behavior of clouds at the L/T transition. Observational data for exoplanet atmosphere characterisation is largely limited to giant exoplanets that are hot because they are near to their star (hot Jupiters) or because they are young and still cooling. For these planets there is good evidence for the presence of CO and H2O absorptions in the IR. Sodium absorption is observed in a number of objects. Reflected light measurements show that some giant exoplanets are very dark, indicating a cloud free atmosphere. However, there is also good evidence for clouds and haze in some other planets. It is also well established that some highly irradiated planets have inflated radii, though the mechanism for this inflation is not yet clear. Some other issues in the composition and structure of giant exoplanet atmospheres such as the occurrence of inverted temperature structures, the presence or absence of CO2and CH4, and the occurrence of high C/O ratios are still the subject of investigation and debate.

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Non-equilibrium Chemistry in the Atmospheres of Brown Dwarfs

Cited by 53 publications

References 20 publications

Young Jupiters are faint: new models of the early evolution of giant planets

Young Jupiters are faint: new models of the early evolution of giant planets

$\mathsf{\varepsilon}$ Indi Ba, Bb: a detailed study of the nearest known brown dwarfs

The Dawes Review 3: The Atmospheres of Extrasolar Planets and Brown Dwarfs

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