SECONDARY ECLIPSE PHOTOMETRY OF WASP-4b WITH WARMSPITZER

Abstract

We present photometry of the giant extrasolar planet WASP-4b at 3.6 and 4.5 µm taken with the Infrared Array Camera on board the Spitzer Space Telescope as part of Spitzer's extended warm mission. We find secondary eclipse depths of 0.319%±0.031% and 0.343%±0.027% for the 3.6 and 4.5 µm bands, respectively and show model emission spectra and pressure-temperature profiles for the planetary atmosphere. These eclipse depths are well fit by model emission spectra with water and other molecules in absorption, similar to those used for TrES-3 and HD 189733b. Depending on our choice of model, these results indicate that this planet has either a weak dayside temperature inversion or no inversion at all. The absence of a strong thermal inversion on this highly irradiated planet is contrary to the idea that highly irradiated planets are expected to have inversions, perhaps due the presence of an unknown absorber in the upper atmosphere. This result might be explained by the modestly enhanced activity level of WASP-4b's G7V host star, which could increase the amount of UV flux received by the planet, therefore reducing the abundance of the unknown stratospheric absorber in the planetary atmosphere as suggested in Knutson et al. (2010). We also find no evidence for an offset in the timing of the secondary eclipse and place a 2σ upper limit on |e cos ω| of 0.0024, which constrains the range of tidal heating models that could explain this planet's inflated radius.

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

“…The models that are best suited to our measurement correspond to atmospheres with null or low amounts of a stratospheric absorber, which leads to non inverted or scarcely inverted atmospheres. A similar result was found in Beerer et al (2011) for observations in the mid-IR. When considering the three measurements, i.e.…”

“…Note that the red model point at 2.16 μm is overlapped by our measurement. The measurements in Beerer et al (2011) are also shown at 3.6, and 4.5 μm. The transmission curves for the three filters are also shown for comparison as dotted lines.…”

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

“…Overall, in conjunction with the Spitzer results the data favor non-inverted water-poor atmospheres for WASP-4b. This result is consistent with the finding of Beerer et al (2011) that WASP-4b does not have a strong thermal inversion. Figure 14 presents the thermal emission spectrum for TrES-3b in the context of representative atmospheric models and past photometric measurements.…”

Variability in the super-Earth 55 Cnc e

“…We also fit a two-dimensional Gaussian to the stellar PRF (Agol et al 2010). We find that determining the centroid position using GCNTRD results in a smaller dispersion of the fitted residuals by 10 to 15% across our dataset, in agreement with other warm Spitzer analyses (Beerer et al 2011). We then perform aperture photometry for each dataset using a modified version of the APER procedure using aperture sizes ranging from 2.2 to 4.4 pixels in 0.2 pixels intervals.…”