Dust in the Photospheric Environment: Unified Cloudy Models of M, L, and T Dwarfs

By T. Tsuji. 2002

144 citations recorded by the source corpus.

We report an attempt to construct unified cloudy models of M, L, and T dwarfs. For this purpose, we first discuss opacities as well as thermochemical properties of the cool and dense matter. Below about 2000 K, refractory material condenses, and dust will play a major role as a source of opacity. Then a major problem in modeling the photospheres of very cool dwarfs is how to treat dust and, especially, how dust could be sustained in the static photosphere for a long time. Under the high density of the photospheres of cool dwarfs, dust forms easily at the condensation temperature, Tcond, but the dust will soon grow larger than its critical radius rcr (at which the Gibbs free energy of condensation attains the maximum) at the critical temperature Tcr. Such large dust grains with rgr ≳ rcr will soon segregate from the gas and precipitate below the photosphere. For this reason, dust exists effectively only in the limited region of Tcr ≲ T ≲ Tcond in the photosphere, and this means that a dust cloud is formed deep in the photosphere rather than in the cooler surface region. With this simple model of the dust cloud, we show that the nongray model photosphere in radiative-convective equilibrium can be extended to Teff values as low as 800 K. Since Tcond ≈ 2000 K for the first condensates such as corundum and iron, the dust cloud is rather warm and necessarily located deeper in the photosphere (τ > 1) for the cooler objects (note that T ≈ Teff at τ ≈ 1). This explains why dust apparently shows little observable effect in T dwarfs. For warmer objects, the dust cloud, which is always formed at the same temperature range of Tcr ≲ T ≲ Tcond, can be located nearer the surface (τ < 1), and, for this reason, L dwarfs appear to be dusty. We show that the recently proposed spectral classification of L and T dwarfs can consistently be interpreted by a single grid of our unified cloudy models with the thin dust cloud deep in the photosphere.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/c3ba9fa8970c2c8f7eca7bd01933ddf3ac90d45f

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Citations in the corpus

LARGE-AMPLITUDE VARIATIONS OF AN L/T TRANSITION BROWN DWARF: MULTI-WAVELENGTH OBSERVATIONS OF PATCHY, HIGH-CONTRAST CLOUD FEATURES (2012, background): “Whereas the predominantly cloudy and predominantly clear end-points of the L/T transition have been well-modeled by various groups (Chabrier et al. 2000; Allard et al. 2001; Tsuji 2002; Allard et al. 2003; Burrows et al. 2006; Saumon & Marley 2008), the transition regime remains poorly understood.”
THE 0.8–14.5 μm SPECTRA OF MID-L TO MID-T DWARFS: DIAGNOSTICS OF EFFECTIVE TEMPERATURE, GRAIN SEDIMENTATION, GAS TRANSPORT, AND SURFACE GRAVITY (2009, background): “As a brown dwarf ages and Teff decreases, the grains condense more deeply in the atmosphere until the cloud layers lie below the photosphere, break apart, or otherwise dissipate (Ackerman & Marley 2001, Tsuji 2002, Burgasser et al. 2002b, Knapp et al. 2004).”
The Spectra of T Dwarfs. II. Red Optical Data (2003, background): “…condensate cloud opacity (Tsuji, Ohnaka, & Aoki 1996; Tsuji et al. 1999; Allard et al. 1996, 2001; Burrows et al. 1997; Ackerman & Marley 2001; Tsuji 2002; however, see Marley et al. 2002; Burrows et al. 2002a), although low-level near-infrared photometric (Enoch, Brown, & Burgasser 2003) and…”
On the Radii of Extrasolar Giant Planets (2003, result): “The assumed absence of grains in the envelopes of low-mass objects is consistent with studies of the detailed observed spectra of T dwarfs (Tsuji 2002).”
Models of very-low-mass stars, brown dwarfs and exoplanets (2011, methodology): “…where gravitational settling is assumed inefficient and dust, often only forsterite, forms in equilibriumwith the gas phase such as the case A of Tsuji (2002), the AMES-Dusty or dusty models of Allard et al. (2001), the cloudy case of Ackerman & Marley (2001), or the case B of Burrows et al.…”
L′ and M′ Photometry of Ultracool Dwarfs (2004, background): “…fluxes of brown dwarfs has advanced considerably during the last few years (Burrows et al. 1997; Chabrier et al. 2000; Allard et al. 2001; Ackerman & Marley 2001; Marley et al. 2002; Burgasser et al. 2002b; Tsuji 2002; Tsuji & Nakajima 2003; Cooper et al. 2003; Burrows, Sudarsky, & Lunine 2003).”
A high-accuracy computed water line list (2006, background): “Nevertheless, considerable progress has been made in recent years in such areas as: convection, molecular abundances, non-LTE effects and dust (Hauschildt et al. 1999; Tsuji 2002; Alexander et al. 2003).”
SpeX SPECTROSCOPY OF UNRESOLVED VERY LOW MASS BINARIES. I. IDENTIFICATION OF 17 CANDIDATE BINARIES STRADDLING THE L DWARF/T DWARF TRANSITION (2009, background): “One-dimensional, static cloud models have been able to explain these trends through the con- finement of condensates which are vertically bound by a balance of gravitational settling and vertical mixing (e.g., Ackerman & Marley 2001; Tsuji 2002; Burrows et al. 2006).”
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).”
INFERENCE OF INHOMOGENEOUS CLOUDS IN AN EXOPLANET ATMOSPHERE (2013, background): “In cloudy L-type brown dwarf atmospheres, the role of clouds has long been appreciated (e.g., Ackerman & Marley 2001; Burrows et al. 2001; Tsuji 2002; Kirkpatrick 2005; Witte et al. 2009) and the observed spectra of such objects cannot be modeled correctly without clouds (Cushing et al. 2008).”
New spectral types L and T (2005, methodology): “As Figure 8 (bottom panel) illustrates, the empirical data show that the temperature range of this color transition is only ∼200 K–300 K. Marley et al. (2002) present a similar approach to Tsuji (2002) by also considering the placement of the condensate clouds relative to the observable photosphere.”
Titanium and Vanadium Chemistry in Low-Mass Dwarf Stars (2002, background): “The effective temperatures of M and L dwarfs depend on atmospheric models, for which several different approaches currently exist (see Ackerman & Marley 2001; Allard et al. 2001; Tsuji 2002).”
MODEL ATMOSPHERES FOR MASSIVE GAS GIANTS WITH THICK CLOUDS: APPLICATION TO THE HR 8799 PLANETS AND PREDICTIONS FOR FUTURE DETECTIONS (2011, background): “Several theoretical studies in the past have also considered cloud properties comparable to our thick cloud models (e.g. Chabrier et al. 2000; Allard et al. 2001; Tsuji 2002 & 2005; Burrows et al. 2006).”
Dust in brown dwarfs - III. Formation and structure of quasi-static cloud layers (2004, unknown): “This generalisation is possibly in conflict with current semi-empirical models of T dwarfs (e.g. Allard et al. 2001; Tsuji 2002) which predict geometrically thin dust layers.”
Near-Infrared Photometry and Spectroscopy of L and T Dwarfs: The Effects of Temperature, Clouds, and Gravity (2004, methodology): “This was subsequently confirmed by models employing more elaborate cloud models (Marley et al. 2002; Tsuji 2002; Allard et al. 2003).”
THE HAWAII INFRARED PARALLAX PROGRAM. I. ULTRACOOL BINARIES AND THE L/T TRANSITION, (2012, background): “…the general properties of the spectra, colors, and magnitudes of late-L to mid-T dwarfs based on prescriptions for the clouds (Marley et al. 2002; Tsuji 2002; Burrows et al. 2006), and parameterized models can be successfully fitted to broad-wavelength observations of individual objects (e.g.,…”
On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets (2014, methodology): “3The ‘Unified Cloud Model’, a defined cloud model (Tsuji 2002).”
The Evolution of L and T Dwarfs in Color-Magnitude Diagrams (2008, background): “…2001; Lodders 2002), increasingly complete molecular opacity databases (Freedman et al. 2008; Sharp & Burrows 2007), extreme resonance line broadening (Burrows et al. 2000; Allard et al. 2005), and particulate cloud models (Allard et al. 2001; Ackerman&Marley 2001; Tsuji 2002; Helling et al. 2008).”