METHANE IN THE ATMOSPHERE OF THE TRANSITING HOT NEPTUNE GJ436B?
- 9 April 2011
- journal article
- research article
- Published by American Astronomical Society in The Astrophysical Journal
- Vol. 731 (1), 16
- https://doi.org/10.1088/0004-637X/731/1/16
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.Keywords
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This publication has 61 references indexed in Scilit:
- A scenario of planet erosion by coronal radiationAstronomy & Astrophysics, 2010
- The HITRAN 2008 molecular spectroscopic databaseJournal of Quantitative Spectroscopy and Radiative Transfer, 2009
- Primary Transit of the Planet HD 189733b at 3.6 and 5.8 μmThe Astrophysical Journal, 2008
- Rayleigh scattering in the transit spectrum of HD 189733bAstronomy & Astrophysics, 2008
- Accurate Spitzer infrared radius measurement for the hot Neptune GJ 436bAstronomy & Astrophysics, 2007
- A Sensitive Search for Variability in Late L Dwarfs: The Quest for WeatherThe Astrophysical Journal, 2006
- A high-accuracy computed water line listMonthly Notices of the Royal Astronomical Society, 2006
- CDSD-1000, the high-temperature carbon dioxide spectroscopic databankJournal of Quantitative Spectroscopy and Radiative Transfer, 2003
- Hot methane spectra for astrophysical applicationsJournal of Quantitative Spectroscopy and Radiative Transfer, 2003
- Theoretical Transmission Spectra during Extrasolar Giant Planet TransitsThe Astrophysical Journal, 2000