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Methane in the atmosphere of the transiting hot Neptune GJ436b?

Beaulieu, J.-P., Tinetti, G., Kipping, D. M., Ribas, I., Barber, R. J., Cho, J. Y.-K., Polichtchouk, I., Tennyson, J., Yurchenko, S. N., Griffith, C. A., Batista, V., Waldmann, I., Miller, S., Carey, S., Mousis, O., Fossey, S. J. and Aylward, A. (2011) Methane in the atmosphere of the transiting hot Neptune GJ436b? The Astrophysical Journal, 731 (1). 16. ISSN 0004-637X

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To link to this article DOI: 10.1088/0004-637X/731/1/16


We present an analysis of seven primary transit observations of the hot Neptune GJ436b at 3.6, 4.5, and 8 μm obtained with the Infrared Array Camera on the Spitzer Space Telescope. After correcting for systematic effects, we fitted the light curves using the Markov Chain Monte Carlo technique. Combining these new data with the EPOXI, Hubble Space Telescope, and ground-based V, I, H, and Ks published observations, the range 0.5-10 μm can be covered. Due to the low level of activity of GJ436, the effect of starspots on the combination of transits at different epochs is negligible at the accuracy of the data set. Representative climate models were calculated by using a three-dimensional, pseudospectral general circulation model with idealized thermal forcing. Simulated transit spectra of GJ436b were generated using line-by-line radiative transfer models including the opacities of the molecular species expected to be present in such a planetary atmosphere. A new, ab-initio-calculated, line list for hot ammonia has been used for the first time. The photometric data observed at multiple wavelengths can be interpreted with methane being the dominant absorption after molecular hydrogen, possibly with minor contributions from ammonia, water, and other molecules. No clear evidence of carbon monoxide and carbon dioxide is found from transit photometry. We discuss this result in the light of a recent paper where photochemical disequilibrium is hypothesized to interpret secondary transit photometric data. We show that the emission photometric data are not incompatible with the presence of abundant methane, but further spectroscopic data are desirable to confirm this scenario.

Item Type:Article
Divisions:No Reading authors. Back catalogue items
Faculty of Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
ID Code:38496
Uncontrolled Keywords:planetary systems; techniques: spectroscopic
Publisher:American Astronomical Society

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