Characterization of the hot Neptune GJ 436b with Spitzer and ground-based observations

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  • 25 July 2007
Abstract
We present Spitzer Space Telescope infrared photometry of a secondary eclipse of the hot Neptune GJ 436b. The observations were obtained using the 8-micron band of the InfraRed Array Camera (IRAC). The data spanning the predicted time of secondary eclipse show a clear flux decrement with the expected shape and duration. The observed eclipse depth of slightly less than 0.5 mmag allows us to estimate a blackbody brightness temperature of Tb = 709 +-17 K at 8 microns. We compare this infrared flux measurement to a model of the planetary thermal emission, and show that this model reproduces properly the observed flux decrement. The timing of the secondary eclipse confirms the non-zero orbital eccentricity of the planet, while also increasing its precision (e = 0.14 +- 0.01). Using additional new spectroscopic and photometric observations allows us to estimate the rotational period of the star and to assess to an high extent the dynamics of the system and the potential presence of another planet.

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