1. Methane in the Atmosphere of the Transiting Hot Neptune GJ436B?
- Author
-
Inna Polichtchouk, Sergei N. Yurchenko, Olivier Mousis, Caitlin A. Griffith, Sean Carey, Giovanna Tinetti, S. Miller, V. Batista, Jonathan Tennyson, Ignasi Ribas, David M. Kipping, R. J. Barber, Ingo Waldmann, S. J. Fossey, J. P. Beaulieu, J. Y-K. Cho, Alan D. Aylward, Institut d'Astrophysique de Paris (IAP), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC), University College of London [London] (UCL), Institut de Ciencies de l'Espai [Barcelona] (ICE-CSIC), Consejo Superior de Investigaciones Científicas [Madrid] (CSIC), Department of Physics and Astronomy [UCL London], Lunar and Planetary Laboratory [Tucson] (LPL), University of Arizona, Univers, Transport, Interfaces, Nanostructures, Atmosphère et environnement, Molécules (UMR 6213) (UTINAM), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC), and Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
010504 meteorology & atmospheric sciences ,Opacity ,[PHYS.ASTR.EP]Physics [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP] ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,7. Clean energy ,01 natural sciences ,Photometry (optics) ,Spitzer Space Telescope ,0103 physical sciences ,Radiative transfer ,Astrophysics::Solar and Stellar Astrophysics ,Hot Neptune ,010303 astronomy & astrophysics ,ComputingMilieux_MISCELLANEOUS ,Astrophysics::Galaxy Astrophysics ,0105 earth and related environmental sciences ,Earth and Planetary Astrophysics (astro-ph.EP) ,Physics ,Atmospheric methane ,Starspot ,Astronomy and Astrophysics ,Light curve ,13. Climate action ,Space and Planetary Science ,Astrophysics::Earth and Planetary Astrophysics ,Astrophysics - Earth and Planetary Astrophysics - 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 (IRAC) 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, HST 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 dataset. Representative climate models were calculated by using a three-dimensional, pseudo-spectral general circulation model with idealised 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, linelist 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 dioxide is found from transit photometry. We discuss this result in the light of a recent paper where photochemical disequilibrium is hypothesised 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., Comment: 19 pages, 10 figures, 1 table, Astrophysical Journal in press
- Published
- 2011