Gilles Chabrier

Evolutionary Models for Very Low-Mass Stars and Brown Dwarfs with Dusty Atmospheres

We present evolutionary calculations for very low-mass stars and brown dwarfs based on synthetic spectra and nongray atmosphere models which include dust formation and opacity, i.e., objects with Teff 2800 K. The interior of the most massive brown dwarfs is shown to develop a conductive core after ~2 Gyr which slows down their cooling. Comparison is made in optical and infrared color-magnitude diagrams with recent late-M and L dwarf observations. The saturation in optical colors and the very red near-infrared colors of these objects are well explained by the onset of dust formation in the atmosphere. Comparison of the faintest presently observed L dwarfs with these dusty evolutionary models suggests that dynamical processes such as turbulent diffusion and gravitational settling are taking place near the photosphere. As the effective temperature decreases below Teff ≈ 1300-1400 K, the colors of these objects move to very blue near-infrared colors, a consequence of the ongoing methane absorption in the infrared. We suggest the possibility of a brown dwarf dearth in J, H, and K color-magnitude diagrams around this temperature.

Evolutionary models for cool brown dwarfs and extrasolar giant planets. The Case of HD 209458

We present evolutionary models for cool brown dwarfs and extra-solar giant planets. The models re- produce the main trends of observed methane dwarfs in near-IR color-magnitude diagrams. We also present evolutionary models for irradiated planets, coupling for the first time irradiated atmosphere profiles and inner structures. We focus on HD 209458-like systems and show that irradiation effects can substantially affect the ra- dius of sub-jovian mass giant planets. Irradiation effects, however, cannot alone explain the large observed radius of HD 209458b. Adopting assumptions which optimise irradiation effects and taking into account the extension of the outer atmospheric layers, we still find � 20% discrepancy between observed and theoretical radii. An extra source of energy seems to be required to explain the observed value of the first transit planet.

Evolutionary models for low-mass stars and brown dwarfs: Uncertainties and limits at very young ages

We analyse pre-Main Sequence evolutionary tracks for low mass stars with masses

New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit

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THEORY OF LOW-MASS STARS AND SUBSTELLAR OBJECTS

based on the Baraffe et al. (1998) input physics. We also extend the recent Chabrier et al. (2000) evolutionary models based on dusty atmosphere to young brown dwarfs down to one mass of Jupiter. We analyse current theoretical uncertainties due to molecular line lists, convection and initial conditions. Simple tests on initial conditions show the high uncertainties of models at ages

The Galactic Disk Mass Budget. I. Stellar Mass Function and Density

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Evolution of low-mass star and brown dwarf eclipsing binaries

1 Myr. We find a significant sensitivity of atmosphere profiles to the treatment of convection at low gravity and

Structure and evolution of super-Earth to super-Jupiter exoplanets: I. heavy element enrichment in the interior

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Activity in Very Cool Stars: Magnetic Dissipation in Late M and L Dwarf Atmospheres

K, whereas it vanishes as gravity increases. This effect adds another source of uncertainty on evolutionary tracks at very early phases. We show that at low surface gravity (

EPISODIC ACCRETION AT EARLY STAGES OF EVOLUTION OF LOW-MASS STARS AND BROWN DWARFS: A SOLUTION FOR THE OBSERVED LUMINOSITY SPREAD IN H-R DIAGRAMS?

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