Department of Astronomy and AstrophysicsP. Universidad Católica de Chile.
Av. Vicuña Mackenna 4860,
2 European Southern Observatory, Av. Alonso de Córdova 3107, Casilla 19, Santiago 19001, Chile
3 Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
4 Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
5 ESA-STScI, 3700 San Martin Drive, Batlimore, MD 21218, USA
6 Department of Astronomy, Universidad de Concepción, Casilla 160-C, Concepción, Chile
7 Obserwatorium Astronomiczne Uniwersytetu Warszawskiego, Aleje Ujazdowskie 4, 00-478 Warszawa, Poland
Accepted: 30 March 2011
Context. Secondary eclipses are a powerful tool to measure directly the thermal emission from extrasolar planets, and to constrain their type and physical parameters.
Aims. We started a project to obtain reliable broad-band measurements of the thermal emission of transiting exoplanets.
Methods. Ground-based high-cadence near-infrared relative photometry was used to obtain a sub-millimagnitude precision light curve of a secondary eclipse of WASP-4b – a 1.12 MJ hot Jupiter on a 1.34 day orbit around G7V star.
Results. The data show a clear ≥10σ detection of the planet’s thermal emission at 2.2 μm. The calculated thermal emission corresponds to a fractional eclipse depth of %, with a related brightness temperature in KS of TB = 1995 ± 40 K, centered at HJD. We could set a limit on the eccentricity of ecosω = 0.0027 ± 0.0018, compatible with a near-circular orbit.
Conclusions. The calculated brightness temperature and the specific models suggest a highly inefficient redistribution of heat from the day-side to the night-side of the planet, and a consequent emission mainly from the day-side. The high-cadence ground-based technique is capable of detecting the faint signal of the secondary eclipse of extrasolar planets, which makes it a valuable complement to space-based mid-IR observations.
Key words: planetary systems / eclipses / stars: individual: WASP-4b / techniques: photometric
Based on observations collected at the European Southern Observatory, Chile. Programme 083.C-0528.
Full Table 1 is only available at CDS via anonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/530/A5
© ESO, 2011