Atmospheric composition and structure of HD209458b

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Atmospheric composition and structure of HD209458b

Post by Sirius_Alpha on 1st September 2008, 3:55 pm

Atmospheric composition and structure of HD209458b

Abstract wrote:Transiting planets like HD209458b offer a unique opportunity to scrutinize their atmospheric composition and structure. Transit spectroscopy probes the transition region between the day and night sides, called limb. We present a re-analysis of existing archived HST/STIS transmission spectra of HD209458b's atmosphere. From these observations we: Identify H2 Rayleigh scattering, derive the absolute Sodium abundance and quantify its depletion in the upper atmosphere, extract a stratospheric T-P profile with a temperature inversion and explain broad band absorptions with the presence of TiO and VO molecules in the atmosphere of this planet.

Some results from the paper:

(a) Rayleigh scattering. The feature in NUV, at wavelength lambda =< 5000 Angstroms, was first reported by Ballester et al. 2007 and explained by the absorption of a hot hydrogen layer within the atmosphere. Here we propose an alternative explanation invoking the Rayleigh scattering by H_2 molecules.

(b) Na depletion and atmospheric structure. Within the same datasets, we find that the Na spectral line profile is characterized by a wide absorption with a sharp transition to a narrow absorption profile at higher altitudes values. This sharp transition is interpreted by condensation or ionization which deplete Na atoms in the upper atmosphere...

(c) TiO/VO. A third broad band absorption feature in the range 6200 Angstroms - 8000 Angstroms appears on the absorption depth spectrum and is still unexplained. Although no typical TiO and VO spectral signatures have been identified unambiguously in the observed spectrum, we suggest that the opacities of these molecules are the best candidates to explain the remaining continuous broad band absorption observed in this wavelength domain. Using the P-T profile from Sing et al. 2008b, we derived upper limits for the Tio and VO abundances. We find that the abundance of TiO should be around 10-4 to 10-3 solar, and the abundance VO around 10-3 to 10-2 solar.

Our possible detection of TiO/VO and Na I in the hot atmosphere of HD 209458 b confirm that this planet is located in the transition region between the [pM Class and pL class]

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