A ground-based K S-band detection of the thermal emission from the transiting exoplanet WASP-4b

C. Cáceres, V. D. Ivanov, D. Minniti, Adam S. Burrows, F. Selman, C. Melo, D. Naef, E. Mason, G. Pietrzynski

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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 0.185+0.014-0.013%, with a related brightness temperature in KS of TB = 1995 ± 40 K, centered at TC = 2455102.61162+0.00071 -0.00077 HJD. We could set a limit on the eccentricity of e cos w = 0.0027 ± 0.0018, compatible with a nearcircular 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.

Original languageEnglish (US)
Article numberA5
JournalAstronomy and Astrophysics
StatePublished - 2011

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • eclipses
  • planetary systems
  • stars: individual: WASP-4b
  • techniques: photometric


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