Exoplanets and Stellar Physics

Abstract:

Abstract:

We determine the observability in transmission of inhomogeneous cloud cover on the limbs of hot Jupiters through post-processing a general circulation model to include cloud distributions computed using a cloud microphysics model. We find that both the east and west limbs often form clouds, but that the different properties of these clouds enhance the limb-to-limb differences compared to the clear case. Using the James Webb Space Telescope, it should be possible to detect the presence of cloud inhomogeneities by comparing the shape of the transit light curve at multiple wavelengths because inhomogeneous clouds impart a characteristic, wavelength-dependent signature. This method is statistically robust even with limited wavelength coverage, uncertainty on limb-darkening coefficients, and imprecise transit times. We predict that the short-wavelength slope varies strongly with temperature. The hot limbs of the hottest planets form higher-altitude clouds composed of smaller particles, leading to a strong Rayleigh slope. The near-infrared spectral features of clouds are almost always detectable, even when no spectral slope is visible in the optical. In some of our models a spectral window between 5 and 9 μm can be used to probe through the clouds and detect chemical spectral features. Our cloud particle size distributions are not lognormal and differ from species to species. Using the area- or mass-weighted particle size significantly alters the relative strength of the cloud spectral features compared to using the predicted size distribution. Finally, the cloud content of a given planet is sensitive to a species' desorption energy and contact angle, two parameters that could be constrained experimentally in the future.

Abstract:

Abstract We calculate the dynamical tides raised by a close planetary companion on non–rotating stars of 1 M⊙ and 1.4 M⊙. Using the Henyey method, we solve the fully non–adiabatic equations throughout the star. The horizontal Lagrangian displacement is found to be 10 to 100 times larger than the equilibrium tide value in a thin region near the surface of the star. This is because non–adiabatic effects dominate in a region that extends from below the outer edge of the convection zone up to the stellar surface, and the equilibrium tide approximation is inconsistent with non–adiabaticity. Although this approximation generally applies in the low frequency limit, it also fails in the parts of the convection zone where the forcing frequency is small but larger than the Brunt-Väisälä frequency. We derive analytical estimates which give a good approximation to the numerical values of the magnitude of the ratio of the horizontal and radial displacements at the surface. The relative surface flux perturbation is also significant, on the order of 0.1% for a system modelled on 51 Pegasi b. Observations affected by the horizontal displacement may therefore be more achievable than previously thought, and brightness perturbations may be the result of flux perturbations rather than due to the radial displacement. We discuss the implication of this on the possibility of detecting such tidally excited oscillations, including the prospect of utilising the large horizontal motion for observations of systems such as 51 Pegasi.