A PATCHY CLOUD MODEL FOR THE L TO T DWARF TRANSITION

By M. Marley, D. Saumon, C. Goldblatt. 2010

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One mechanism suggested for the L to T dwarf spectral type transition is the appearance of relatively cloud-free regions across the disk of brown dwarfs as they cool. The existence of partly cloudy regions has been supported by evidence for variability in dwarfs in the late L to early T spectral range, but no self-consistent atmosphere models of such partly cloudy objects have yet been constructed. Here, we present a new approach for consistently modeling partly cloudy brown dwarfs and giant planets. We find that even a small fraction of cloud holes dramatically alter the atmospheric thermal profile, spectra, and photometric colors of a given object. With decreasing cloudiness objects briskly become bluer in J − K and brighten in J band, as is observed at the L/T transition. Model spectra of partly cloudy objects are similar to our models with globally homogenous, but thinner, clouds. Hence, spectra alone may not be sufficient to distinguish partial cloudiness although variability and polarization measurements are potential observational signatures. Finally, we note that partial cloud cover may be an alternative explanation for the blue L dwarfs.

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

View Paper: https://www.semanticscholar.org/paper/83d118bee02f3b1f482b5a9cbfbfaa8a2d0336ed

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Citations in the corpus

TRANSITIONS IN THE CLOUD COMPOSITION OF HOT JUPITERS (2016, background): “This is surprising since over the same range of effective temperatures a strong correlation between temperature and cloudiness has been established for brown dwarfs (Kirkpatrick 2005; Marley et al. 2010).”
3D mixing in hot Jupiters atmospheres. I. Application to the day/night cold trap in HD 209458b (2013, methodology): “Hazes could also show a similar behavior, leading to planetary spectra that might be better explained with the combinationof two different (cloudy and cloudless) 1D models—as is the case in recent models of brown dwarfs (e.g., Marley et al. 2010; Burrows et al. 2011).”
GASEOUS MEAN OPACITIES FOR GIANT PLANET AND ULTRACOOL DWARF ATMOSPHERES OVER A RANGE OF METALLICITIES AND TEMPERATURES (2014, background): “…et al. (2008) (hereafter, F08) we presented a detailed discussion of atomic and molecular line opacities used by our group in modeling the atmospheres of brown dwarfs and giant planets (e.g. Marley et al. 2002; Fortney et al. 2005; Saumon & Marley 2008; Fortney et al. 2008; Marley et al. 2010).”
WEATHER ON OTHER WORLDS. II. SURVEY RESULTS: SPOTS ARE UBIQUITOUS ON L AND T DWARFS (2014, background): “Ackerman & Marley (2001) proposed that such heterogeneous cloud structures may be present in brown dwarf atmospheres, leading to rotationally modulated flux variations and explaining many of the unusual characteristics of the L dwarf/T dwarf transition (Burgasser et al. 2002; Marley et al. 2010).”
FUNDAMENTAL PARAMETERS AND SPECTRAL ENERGY DISTRIBUTIONS OF YOUNG AND FIELD AGE OBJECTS WITH MASSES SPANNING THE STELLAR TO PLANETARY REGIME (2015, background): “Lbol is almost constant through the L/T transition as condensates rain out of the photosphere, quickly evolving through spectral type as deeper and brighter layers are exposed (Marley et al. 2010).”
HST SPECTRAL MAPPING OF L/T TRANSITION BROWN DWARFS REVEALS CLOUD THICKNESS VARIATIONS (2013, methodology): “…models (e.g. Ackerman & Marley 2001; Burgasser et al. 2002; Skemer et al. 2012; Barman et al. 2011a,b; Burrows et al. 2006; Madhusudhan et al. 2011; Marley et al. 2010 and progress has been made in spectroscopic modeling to separate or constrain the impact of cloud structure from other parameters…”
CLOUDS AND CHEMISTRY IN THE ATMOSPHERE OF EXTRASOLAR PLANET HR8799b (2011, background): “Nevertheless, the “patchiness” of clouds can be explored in an ad hoc fashion via a combination of cloudy and cloud-free models (Burgasser et al. 2002) or, more recently and selfconsistently, within a single one-dimensional model (Marley et al. 2010).”
MASSES, RADII, AND CLOUD PROPERTIES OF THE HR 8799 PLANETS (2012, background): “Ackerman & Marley (2001), Burgasser et al. (2002), and Marley et al. (2010) have suggested that the arrival of holes in brown dwarf clouds, perhaps due to the clouds passing through a dynamical boundary in the atmosphere, might also be responsible for the L to T transition.”
H− Opacity and Water Dissociation in the Dayside Atmosphere of the Very Hot Gas Giant WASP-18b (2018, methodology): “The code has been validated against analytic solutions and agrees to within 3% and against the brown dwarf models of Marley et al. (2010).”
A COMBINED SUBARU/VLT/MMT 1–5 μm STUDY OF PLANETS ORBITING HR 8799: IMPLICATIONS FOR ATMOSPHERIC PROPERTIES, MASSES, AND FORMATION (2011, methodology): “8 We leave a detailed construction of such models to a future paper (Madhusudhan et al., in prep.) but here we qualitatively explore how intermediate cases may affect the predicted planet spectrum (see also Marley et al. 2010).”
NEGLECTED CLOUDS IN T AND Y DWARF ATMOSPHERES (2012, background): “Marley et al. (2010) show that this transition could potentially be explained by the br aking up of these cloud layers into patchy clouds, but the details of the transition are still very much unknown.”
LARGE-AMPLITUDE VARIATIONS OF AN L/T TRANSITION BROWN DWARF: MULTI-WAVELENGTH OBSERVATIONS OF PATCHY, HIGH-CONTRAST CLOUD FEATURES (2012, background): “The drawback is that combinations of independent 1D atmosphere models may possess incompatible T-P profiles, and we are therefore not guaranteed to arrive at physically plausible configurations (see the discussion within Marley et al. 2010).”
THE HAWAII INFRARED PARALLAX PROGRAM. I. ULTRACOOL BINARIES AND THE L/T TRANSITION, (2012, background): “…the late-L and early-T dwarfs, including non-equilibrium (dynamic) processes such rapid particle growth/sedimentation (Knapp et al. 2004; Stephens et al. 2009) and cloud disruption leading to spatially inhomogeneous photospheres (Ackerman & Marley 2001; Burgasser et al. 2002; Marley et al. 2010).”
THE INFLUENCE OF NONUNIFORM CLOUD COVER ON TRANSIT TRANSMISSION SPECTRA (2015, methodology): “Similar processes are presumed to happen in Brown dwarf atmospheres (Burgasser et al. 2002; Marley et al. 2010; Zhang & Showman 2014), where observations are strongly suggestive of non-uniform cloud cover (Buenzli et al. 2012;14; Radigan et al. 2012;14; Crossfield et al. 2014; Apai et al. 2013;…”
FURTHER DEFINING SPECTRAL TYPE “Y” AND EXPLORING THE LOW-MASS END OF THE FIELD BROWN DWARF MASS FUNCTION (2012, background): “The physical cause for this brightening may be due to patchy clouds in the atmospheres of these objects (Marley et al. 2010).”
On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets (2014, background): “Indeed, a variety of patchy cloud models have demonstrated that, in many cases, observed variability can be explained by changes in cloud distribution and thickness (Marley et al. 2010; Apai et al. 2013; Burgasser et al. 2014; Morley et al. 2014a).”