Beaulieu, J. -P. and Tinetti, G. and Kipping, D. M. and Ribas, I. and Barber, R. J. and Cho, J. Y. -K. and Polichtchouk, I. and Tennyson, J. and Yurchenko, S. N. and Griffith, C. A. and Batista, V. and Waldmann, I. and Miller, S. and Carey, S. and Mousis, O. and Fossey, S. J. and Aylward, A. (2011) Methane in the Atmosphere of the Transiting Hot Neptune GJ436B? Astrophysical Journal, 731 (1). Art. No. 16. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20110506-141703127
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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 K_s 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.
|Additional Information:||© 2011 American Astronomical Society. Received 2010 July 1; accepted 2011 February 4; published 2011 March 17. G.T. is supported by a Royal Society University Research Fellowship, D.M.K. and I.W. by STFC, R.J.B. by the Leverhulme Trust, J.Y.-K.C. is supported by the STFC PP/ E001858/1 grant. I.R. acknowledges support from the Spanish Ministerio de Ciencia e Innovaciόn via grant AYA2009-06934. We acknowledge the support by ANR-06-BLAN-0416 and the “Programme Origine des Planètes et de la Vie.” This work is based on observations made with the Spitzer Space Telescope which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.|
|Subject Keywords:||planetary systems; techniques: spectroscopic|
|Classification Code:||PACS: 97.82.-j; 95.30.Jx. 95.30.Ft; 95.30.Ky; 95.10.Gi|
|Official Citation:||Methane in the Atmosphere of the Transiting Hot Neptune GJ436B? J.-P. Beaulieu, G. Tinetti, D. M. Kipping, I. Ribas, R. J. Barber, J. Y.-K. Cho, I. Polichtchouk, J. Tennyson, S. N. Yurchenko, C. A. Griffith, V. Batista, I. Waldmann, S. Miller, S. Carey, O. Mousis, S. J. Fossey and A. Aylward doi: 10.1088/0004-637X/731/1/16|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||09 May 2011 18:36|
|Last Modified:||26 Dec 2012 13:13|
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