UCL logo

UCL Discovery

UCL home » Library Services » Electronic resources » UCL Discovery

Methane in the Atmosphere of the Transiting Hot Neptune GJ436b?

Beaulieu, JP; Tinetti, G; Kipping, DM; Ribas, I; Barber, RJ; Cho, JYK; ... Aylward, A; + view all (2011) Methane in the Atmosphere of the Transiting Hot Neptune GJ436b? Astrophysical Journal , 731 (1) , Article 16. 10.1088/0004-637X/731/1/16. Green and gold open access

[img]
Preview
PDF - Requires a PDF viewer such as GSview, Xpdf or Adobe Acrobat Reader
2063Kb

Abstract

We present an analysis of seven primary transit observations of the hot Neptune GJ436b at 3.6, 4.5, and 8 mu m 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 K-s published observations, the range 0.5-10 mu m 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.

Type:Article
Title:Methane in the Atmosphere of the Transiting Hot Neptune GJ436b?
Open access status:An open access publication. A version is also available from UCL Discovery.
DOI:10.1088/0004-637X/731/1/16
Publisher version:http://dx.doi.org/10.1088/0004-637X/731/1/16
Language:English
Additional information:© 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
Keywords:Planetary systems, Spectroscopic techniques, Extrasolar giant planets, Hubble-space-telescope, Transmission spectra, HD 189733B, GJ 436B, M-dwarfs, MU-M, Spitzer, Temperature, Models
UCL classification:UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Physics and Astronomy
UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Science and Technology Studies

View download statistics for this item

Archive Staff Only: edit this record