Balancing the energy budget of short-period giant planets: evidence for reflective clouds and optical absorbers

Abstract

We consider fifty transiting short-period giant planets for which eclipse depths have been measured at multiple infrared wavelengths. The aggregate dayside emission spectrum of these planets exhibits no molecular features, nor is brightness temperature greater in the nearinfrared. We combine brightness temperatures at various infrared wavelengths to estimate the dayside effective temperature of each planet. We find that dayside temperatures are proportional to irradiation temperatures, indicating modest Bond albedo and no internal energy sources, plus weak evidence that dayside temperatures of the hottest planets are disproportionately high. We place joint constraints on Bond albedo, A B , and day-to-night transport efficiency, ε, for six planets by combining thermal eclipse and phase variation measurements (HD 149026b, HD 189733b, HD 209458b, WASP-12b, WASP-18b, and WASP-43b). We confirm that planets with high irradiation temperatures have low heat transport efficiency, and that WASP-43b has inexplicably poor transport; these results are statistically significant even if the precision of single-eclipse measurements has been overstated by a factor of three. Lastly, we attempt to break the A B -ε degeneracy for nine planets with both thermal and optical eclipse observations, but no thermal phase measurements. We find a systematic offset between Bond albedos inferred from thermal phase variations (A B ≈ 0.35) and geometric albedos extracted from visible light measurements (A g ≈ 0.1). These observations can be reconciled if most hot Jupiters have clouds that reflect 30-50 per cent of incident near-infrared radiation, as well as optical absorbers in the cloud particles or above the cloud deck.

Dynamical Constraints on the Core Mass of Hot Jupiter Hat-P-13b

“…For HAT-P-13b T 0 =2469 K, yielding a predicted T d ≈2090 K(from Figure 2 of Schwartz & Cowan 2015), which is 2σ above the effective dayside temperature we measure (1906±93 K). The T d /T 0 that we obtain for HAT-P-13b (0.7720±0.0377) indicates relatively efficient redistribution of energy to the night side for the case of zero Bond albedo(see Figure 7 of Cowan & Agol 2011), in good agreement with our findings in Section 3.3.…”

“…We therefore conclude that uncertainties in the internal heat dissipation introduce modest, but not overwhelming, uncertainties in the estimate of M core,b (i.e., lack of knowledge of the heat dissipation yields uncertainties that are within the 1σ errors from the observational uncertainties). Schwartz & Cowan (2015) compare the irradiation temperatures (…”

“…The HAT-P-13 system will likely provide invaluable leverage when exploring the relationship between host star and planetary metallicity. In addition, full-orbit phase curve observations with Spitzer would also allow us to break degeneracies between the planetʼs dayside albedo and the efficiency of its atmospheric circulation(e.g., Schwartz & Cowan 2015). The possibility of independently constraining both the core mass and the atmospheric properties of HAT-P-13b makes this planet an ideal target for future observations.…”

An Ultra-short Period Rocky Super-Earth with a Secondary Eclipse and a Neptune-like Companion around K2-141

“…This seems to be the case with Kepler-78b (Sanchis-Ojeda et al 2013) and Kepler-10b (Esteves et al 2015), even though a non-negligible nightside temperature for the latter has been reported by Fogtmann-Schulz et al (2014). The geometric albedos of both planets could not be well constrained because of the degeneracy between thermal and reflected light in the Kepler bandpass, which could be broken with observations of the occultation and phase curve at IR wavelengths (e.g., Schwartz & Cowan 2015). Noteworthy is the attempt by Rouan et al (2011) to use a lava-ocean model to interpret the optical occultation and phase curve of Kepler-10b.…”

Probing exoplanet clouds with optical phase curves

“…At infrared wavelengths the measured flux from hot planets is typically dominated by thermal emission. In the optical, both thermal emission and reflected starlight contribute, with the relative size of the contributions dependent on the measurement wavelength as well as on the temperature of the atmosphere and the occurrence of condensates (20)(21)(22)(23)(24)(25).…”