Accurate Spitzer infrared radius measurement for the hot Neptune GJ 436b
M. Gillon (1, 2), B.-O. Demory (1), T. Barman (3), X. Bonfils (4), T., Mazeh (5), F. Pont (1), S. Udry (1), M. Mayor (1), D. Queloz (1) ((1), Observatoire de l'Universite de Geneve, Sauverny, Switzerland, (2) Institut, d'Astrophysique et de Geophysique, Universite de Liege
TL;DR
This study uses Spitzer infrared photometry to precisely measure the radius and orbital parameters of the hot Neptune GJ 436b, revealing the planet's likely internal structure.
Contribution
First precise infrared transit measurement of GJ 436b enabling accurate radius and orbital parameter determination.
Findings
Planet radius: 4.19 (+0.21-0.16) Earth radii
Orbital inclination: 85.90 (+0.19-0.18) degrees
Small H/He envelope needed in models
Abstract
We present Spitzer Space Telescope infrared photometry of a primary transit of the hot Neptune GJ 436b. The observations were obtained using the 8 microns band of the InfraRed Array Camera (IRAC). The high accuracy of the transit data and the weak limb-darkening in the 8 microns IRAC band allow us to derive (assuming M = 0.44 +- 0.04 Msun for the primary) a precise value for the planetary radius (4.19 +0.21-0.16 Rearth), the stellar radius (0.463 +0.022-0.017 Rsun), the orbital inclination (85.90 +0.19-0.18 degrees) and transit timing (2454280.78186 +0.00015-0.00008 HJD). Assuming current planet models, an internal structure similar to that of Neptune with a small H/He envelope is necessary to account for the measured radius of GJ 436b.
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