Abstract
Within the next few years, GAIA and several instruments aiming to image extrasolar planets will be ready. In parallel, low-mass planets are being sought around red dwarfs, which offer more favourable conditions, for both radial velocity detection and transit studies, than solar-type stars. In this paper, the authors of a model atmosphere code that has allowed the detection of water vapour in the atmosphere of hot Jupiters review recent advances in modelling the stellar to substellar transition. The revised solar oxygen abundances and cloud model allow the photometric and spectroscopic properties of this transition to be reproduced for the first time. Also presented are highlight results of a model atmosphere grid for stars, brown dwarfs and extrasolar planets.
Highlights
Since the spectroscopic observations of very-low-mass stars (VLMs, late 1980s), brown dwarfs and extrasolar planets have become available, the MK spectral classification has had to be extended beyond K and M to the newly defined classes L and T
The K dwarfs show the onset of formation of metal hydrides, TiO and CO, while water vapour forms in early M dwarfs (Teff ∼ 3900–2000 K), and methane, ammonia and carbon dioxide are detected in late-type brown dwarfs (Teff ∼ 300–1600 K) and in extrasolar giant planets
We report progress on the development of a new model atmosphere grid for stars, brown dwarfs and young planets, named BT-Settl
Summary
Since the spectroscopic observations of very-low-mass stars (VLMs, late 1980s), brown dwarfs (mid-1990s) and extrasolar planets (mid-2000s) have become available, the MK spectral classification has had to be extended beyond K and M to the newly defined classes L and T. The K dwarfs show the onset of formation of metal hydrides (starting around Teff ∼ 4500 K), TiO and CO (below Teff ∼ 4000 K), while water vapour forms in early M dwarfs (Teff ∼ 3900–2000 K), and methane, ammonia and carbon dioxide are detected in late-type brown dwarfs (Teff ∼ 300–1600 K) and in extrasolar giant planets. The latter are observed either by transit (Teff ∼ 1000–2000 K, depending on the spectral type of the central star and the distance to the star) or by imaging (young planets of Teff ∼ 300–2000 K, depending on their mass and age). In parallel with detailed radiative transfer in an assumed static environment, hydrodynamical simulations have been developed to reach a realistic representation of the granulation and its induced line shifts for the Sun and Sun-like stars [8] by using a non-grey (multi-group binning of opacities) radiative transfer with a pure blackbody source function (scattering is neglected)
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