A ground-basedK_S-band detection of the thermal emission from the transiting exoplanet WASP-4b

Abstract

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 M J 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 K S of T B = 1995 ± 40 K, centered at T C = 2455102.61162 +0.00071 −0.00077 HJD. We could set a limit on the eccentricity of e cos ω = 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.

ATMOSPHERIC CHARACTERIZATION OF FIVE HOT JUPITERS WITH THE WIDE FIELD CAMERA 3 ON THEHUBBLE SPACE TELESCOPE

“…13.-WASP-4b thermal emission spectrum. Also plotted are results from past broadband eclipse measurements in Beerer et al (2011) and Cáceres et al (2011). Overplotted are a solar-composition atmosphere (brown) and a carbon-rich atmosphere (green) that lack thermal inversions, and a thermally inverted solar-composition atmosphere (red).…”

Ground-based transit observations of the super-Earth GJ 1214 b

“…To extract the apparent fluxes from the reduced images we carried out aperture photometry with the IRAF Digiphot package 1 . Led by our previous experience with stare-mode NIR data, we removed the sky by measuring it in circular annuli, contiguous to the aperture centered on the object (Cáceres et al 2009(Cáceres et al , 2011. We performed photometry for different aperture radii, ranging from 4.0 to 14.0 px, in steps of 0.5 px, and selected the combination of source and sky apertures that minimizes the root mean square (rms) of the final differential light curve: target and reference aperture radii of 2.32 arcsec, and a sky annulus with 4.9 arcsec inner radius and 3.3 arcsec width.…”

Gemini/GMOS Transmission Spectral Survey: Complete Optical Transmission Spectrum of the Hot Jupiter WASP-4b

“…Despite detailed study of the WASP-4 planetary system, however, secondary eclipse observations have not constrained the composition (Beerer et al 2011;Cáceres et al 2011;Ranjan et al 2014) and there are no robust transmission spectral data available for this planet. The transmission spectrum of WASP-4b has been observed with WFC3 in the near-infrared but problems with the treatment of detector non-linearity meant that a robust transmission spectrum could not be obtained (Ranjan et al 2014).…”