L and T Dwarf Models and the L to T Transition

By Adam Burrows, D. Sudarsky, I. Hubeny. 2005

312 citations recorded by the source corpus.

Using a model for refractory clouds, a novel algorithm for handling them, and the latest gas-phase molecular opacities, we have produced a new series of L and T dwarf spectral and atmosphere models as a function of gravity and metallicity, spanning the Teff range from 2200 to 700 K. The correspondence with observed spectra and infrared colors for early and mid-L dwarfs and for mid- to late T dwarfs is good. We find that the width in infrared color-magnitude diagrams of both the T and L dwarf branches is naturally explained by reasonable variations in gravity and therefore that gravity is the ``second parameter" of the L-T dwarf sequence. We investigate the dependence of theoretical dwarf spectra and color-magnitude diagrams on various cloud properties, such as particle size and cloud spatial distribution. In the region of the L → T transition, we find that no single combination of cloud particle size and gravity can be made to fit all the observed data. Our results suggest that current ignorance of detailed cloud meteorology renders ambiguous the extraction of various physical quantities such as Teff and gravity for mid-L to early T dwarfs. Nevertheless, for decreasing Teff, we capture with some accuracy the major spectral features and signatures observed. We speculate that the subdwarf branch of the L dwarfs would be narrower in effective temperature and that for low enough metallicity the L dwarfs would disappear altogether as a spectroscopic class. Furthermore, we note that the new, lower solar oxygen abundances of Allende-Prieto and coworkers produce better fits to brown dwarf data than do the older values. Finally, we discuss various issues in cloud physics and modeling and speculate on how a better correspondence between theory and observation in the problematic L → T transition region could be achieved.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/70645971fa4955d575329ae5fefceae6e603a6d7

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In Astronomy and Astrophysics

1. Michael C. Liu
2. M. Marley
3. A. Burgasser
4. T. Dupuy
5. Jon Fortney
6. J. D. Kirkpatrick
7. K. Luhman
8. D. Saumon

In Instrumentation

1. Michael C. Liu
2. A. Burgasser
3. J. D. Kirkpatrick
4. M. Marley
5. T. Dupuy
6. K. Luhman
7. Jon Fortney
8. Kelle Cruz

Citations in the corpus

• PHOTOMETRIC VARIABILITY OF THE T2.5 BROWN DWARF SIMP J013656.5+093347: EVIDENCE FOR EVOLVING WEATHER PATTERNS (2009, methodology): “Also, the overall behavior between the Allard et al. (2003) and Burrows et al. (2006) models is consistent.”
• LARGE-AMPLITUDE VARIATIONS OF AN L/T TRANSITION BROWN DWARF: MULTI-WAVELENGTH OBSERVATIONS OF PATCHY, HIGH-CONTRAST CLOUD FEATURES (2012, methodology): “The SETTL/COND and cloudy/clear models of Allard et al. (2003) and Burrows et al. (2006) are equally able to reproduce the photometric variations, requiring somewhat lower temperature contrasts when T1 .”
• THE HAWAII INFRARED PARALLAX PROGRAM. I. ULTRACOOL BINARIES AND THE L/T TRANSITION, (2012, background): “…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., Cushing et…”
• The rp-Process in Neutrino-driven Winds (2006, background): “Furthermore, some other mechanisms that increase entropy have been also proposed (e.g., Qian &Woosley 1996; Thompson 2003; Suzuki & Nagataki 2005; Burrows et al. 2006).”
• Models of very-low-mass stars, brown dwarfs and exoplanets (2011, background): “…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. (2006).”
• THE INFLUENCE OF NONUNIFORM CLOUD COVER ON TRANSIT TRANSMISSION SPECTRA (2015, background): “…constraints on other atmospheric properties like temperatures and abundances (Ackerman & Marley 2001; Kirpatrick 2005; Cushing et al. 2008; Burrows et al. 2006; Howe & Burrows 2012; Morley et al. 2013;15; Kriedberg et al. 2014a;15; Vahidinia et al. 2014; Knutson et al. 2014; Benneke 2015;…”
• LSST: From Science Drivers to Reference Design and Anticipated Data Products (2008, methodology): “SEDs for M, L, and T dwarfs are generated from a combination of spectral models and by stacking spectra from the SDSS (e.g., Cushing et al. 2005, Bochanski et al. 2007, Burrows et al. 2006, Petterson & Hawley 1989, Kowalski et al. 2010).”
• MASSES, RADII, AND CLOUD PROPERTIES OF THE HR 8799 PLANETS (2012, methodology): “Burrows et al. (2006) and Witte et al. (2011) have speculated that the interplay of dynamical and cloud microphysics effects that may occur when the intermediate radiative zone forms or departs may play a role in the transition.”
• A Spitzer Infrared Spectrograph Spectral Sequence of M, L, and T Dwarfs (2004, background): “Models that neglect dust formation produce near-infrared colors that are much bluer than the observations (Allard et al. 2001; Marley et al. 2002; Knapp et al. 2004; Burrows et al. 2006).”
• NEAR-INFRARED SPECTROSCOPY OF THE EXTRASOLAR PLANET HR 8799 b (2010, background): “…are many parameters in the cloud models that can influence the emergent spectra, such as particle size and cloud model prescription (see, e.g., Burrows et al. 2006 and Helling et al. 2008 for detailed discussions), and thus the best-fitting vertical mixing and/or metallicity value may change…”
• A PATCHY CLOUD MODEL FOR THE L TO T DWARF TRANSITION (2010, background): “Burrows et al. (2006) also suggest changes in cloud particle sizes as a possible mechanism.”
• ATMOSPHERIC CHEMISTRY IN GIANT PLANETS, BROWN DWARFS, AND LOW-MASS DWARF STARS. III. IRON, MAGNESIUM, AND SILICON (2010, background): “…1 illustrates model atmospheric profiles for an M dwarf (Teff = 2600 K, log g = 5.0; Tsuji et al. 1996), an L dwarf (Teff = 1800 K, log g = 5.0; Burrows et al. 2006), the hot, closein (Pegasi) planet HD209458b (Teff = 1350 K; Iro et al. 2005), the T dwarf Gliese 229B (Teff = 960 K; Marley et…”
• Discovery of Two T Dwarf Companions with the Spitzer Space Telescope (2006, background): “In contrast, low gravity should cause these colors to become bluer, not redder, according to the theoretical spectra of Burrows et al. (2006).”
• DIRECT IMAGING OF A COLD JOVIAN EXOPLANET IN ORBIT AROUND THE SUN-LIKE STAR GJ 504 (2013, background): “It deviates from this sequence in H − Ks, due to overluminosity in Ksband, which is probably due to a low surface gravity or enrichment in heavy elements, both of which can reproduce such an effect (Burrows et al. 2006).”