Ammonia as a Tracer of Chemical Equilibrium in the T7.5 Dwarf Gliese 570D

By D. Saumon, M. Marley, M. Cushing, S. Leggett, T. Roellig, K. Lodders, R. Freedman. 2006

163 citations recorded by the source corpus.

We present the first analysis of an optical to mid-infrared spectrum of the T7.5 dwarf Gliese 570D with model atmospheres, synthetic spectra, and brown dwarf evolution sequences. We obtain precise values for the basic parameters of Gl 570D: Teff = 800-820 K, log g (cm s-2) = 5.09-5.23, and log = -5.525 to -5.551. The Spitzer Infrared Spectrograph (IRS) spectrum shows prominent features of ammonia (NH3) that can only be fitted by reducing the abundance of NH3 by about 1 order of magnitude from the value obtained with chemical-equilibrium models. We model departures from chemical equilibrium in the atmosphere of Gl 570D by considering the kinetics of nitrogen and carbon chemistry in the presence of vertical mixing. The resulting model spectrum reproduces the data very well.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/583859ee8c50194e0c92c2d8fb8e4715c4187002

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In Astronomy and Astrophysics

1. M. Marley
2. Jon Fortney
3. N. Madhusudhan
4. Michael C. Liu
5. Adam Burrows
6. A. Showman
7. D. Saumon
8. T. Dupuy

Citations in the corpus

• Synthetic Spectra and Colors of Young Giant Planet Atmospheres: Effects of Initial Conditions and Atmospheric Metallicity (2008, methodology): “As discussed by Saumon et al. (2006), the distance, metallicity, and age of the system effectively constrain the physical parameters of the T dwarf Gl 570D.”
• Spitzer IRAC Photometry of M, L, and T Dwarfs (2006, unknown): “More recently, the models have begun to take into account nonequilibrium chemistry (e.g., Noll et al. 1997; Saumon et al. 2000, 2003, 2006; Burrows et al. 2000; Ackerman & Marley 2001; Allard et al. 2001; Lodders & Fegley 2002; Marley et al. 2002; Tsuji 2002).”
• MASSES, RADII, AND CLOUD PROPERTIES OF THE HR 8799 PLANETS (2012, methodology): “…appears that departures from equilibrium are inevitable in the atmospheres of cool brown dwarfs and indeed the phenomenon is well established (e.g., Saumon et al. 2000; Geballe et al. 2001; Hubeny & Burrows 2007; Geballe et al. 2009; Mainzer et al. 2007; Saumon et al. 2006; Stephens et al. 2009).”
• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams (2008, methodology): “99+011613.0, whose SED favors a model with fsed ¼ 4 (Stephens et al. 2008).”
• Models of very-low-mass stars, brown dwarfs and exoplanets (2011, background): “Similarly, ammonia has been shown to be underabundant (Saumon et al. 2006).”
• On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets (2014, methodology): “Indeed signs of NH3 under-abundance compared to the expectations of equilibrium chemistry have already been reported in brown dwarfs (Saumon et al. 2006), which has also been reviewed by Zahnle & Marley (2014).”
• A Unified Theory for the Atmospheres of the Hot and Very Hot Jupiters: Two Classes of Irradiated Atmospheres (2007, methodology): “Recently it has been applied to L- and T-type brown dwarfs (Saumon et al. 2006, 2007; Cushing et al. 2007) and hot Jupiters (Fortney etal.”
• The Influence of Atmospheric Dynamics on the Infrared Spectra and Light Curves of Hot Jupiters (2006, background): “…(Prinn & Barshay 1977; Fegley & Prinn 1985; Fegley & Lodders 1994; Bézard et al. 2002; Visscher & Fegley 2005b) and brown dwarfs (Fegley & Lodders 1996; Noll et al. 1997; Griffith & Yelle 1999; Saumon et al. 2000, 2003, 2006), where vertical mixing can be due to convection and/or eddy diffusion.”
• Discovery of 11 New T Dwarfs in the Two Micron All Sky Survey, Including a Possible L/T Transition Binary (2007, background): “…reproduce the measured indices for the near infrared SpeX prism spectrum of Gliese 570D (Burgasser et al. 2000a), which has parameters of Teff = 782– 821 K, log g = 4.95–5.23 and [Fe/H] = 0.09±0.04, based on empirical measurements and evolutionary models (Geballe et al. 2001; Saumon et al. 2006).”
• A comparison of chemistry and dust cloud formation in ultracool dwarf model atmospheres (2008, unknown): “5 dwarf Gliese 570D imply Keddy ∼ 106 cm2 s−1 (Saumon et al. 2006; Geballe et al. 2008).”
• CAN TiO EXPLAIN THERMAL INVERSIONS IN THE UPPER ATMOSPHERES OF IRRADIATED GIANT PLANETS? (2009, background): “Estimates in the context of brown dwarfs place it in the range 102−106 cm2 s−1 (Saumon et al. 2006, 2007; Griffith & Yelle 1999; Hubeny & Burrows 2007).”
• GASEOUS MEAN OPACITIES FOR GIANT PLANET AND ULTRACOOL DWARF ATMOSPHERES OVER A RANGE OF METALLICITIES AND TEMPERATURES (2014, background): “These effects have been explored in solar system giant planets, exoplanets, and brown dwarfs in many papers (e.g., Prinn & Barshay 1977; Fegley & Lodders 1996; Saumon et al. 2003, 2006; Hubeny & Burrows 2007; Visscher & Moses 2011).”
• Discovery and spectroscopy of the young jovian planet 51 Eri b with the Gemini Planet Imager (2015, unknown): “Deviations from equilibrium chemistry are also now considered important in all substellar objects and may delay the onset of methane dominance in near-IR spectra of young giant planets ( 11 , 89 , 90 ).”
• THE DISCOVERY OF Y DWARFS USING DATA FROM THE WIDE-FIELD INFRARED SURVEY EXPLORER (WISE) (2011, background): “…is not a surprising result given that strong evidence for vertical mixing in the atmospheres of brown dwarfs has been found at longer wavelengths (Saumon et al. 2006, 2007; Leggett et al. 2007b; Burgasser et al. 2008; Leggett et al. 2009; Stephens et al. 2009; Geballe et al. 2009; Cushing et al.…”
• A COMBINED SUBARU/VLT/MMT 1–5 μm STUDY OF PLANETS ORBITING HR 8799: IMPLICATIONS FOR ATMOSPHERIC PROPERTIES, MASSES, AND FORMATION (2011, background): “Hinz et al. (2010) argue that incorporating non-equilibrium chemistry is necessary to reproduce the mid-IR photometry of HR 8799bcd since the chemical equilibrium models they use (Saumon et al. 2006) predict M-band fluxes larger than the upper limits they report.”
• On the Luminosity of Young Jupiters (2006, methodology): “Saumon et al. (2006) have computed a cloud-free grid of atmospheres from Teff = 500–2400K and log g = 3.5–5.5 cm sec −2.”
• CLOUDS AND CHEMISTRY IN THE ATMOSPHERE OF EXTRASOLAR PLANET HR8799b (2011, background): “The spectroscopic detections of CO in several cool T-type brown dwarfs (Noll et al. 1997; Saumon et al. 2000, 2006; Geballe et al. 2009) along with weaker than predicted fluxes from ∼ 4.5 µm ground and space-based photometry (Patten et al. 2006; Leggett et al. 2007) have established disequilibrium…”
• DISEQUILIBRIUM CARBON, OXYGEN, AND NITROGEN CHEMISTRY IN THE ATMOSPHERES OF HD 189733b AND HD 209458b (2011, background): “…Kzz is likely several orders of magnitude greater than the sluggish Kzz ≈ 10 2–104 cm2 s−1 that has often been reported (e.g., Griffith & Yelle 1999; Saumon et al. 2003, 2006; Leggett et al. 2007; Geballe et al. 2009), but also in relation to the implied strength of atmospheric mixing on…”