The migration of single hot Jupiters: Balance of evidence tips towards dynamical and tidal evolution

In this thesis, we revisit the seventeen year old question of how hot Jupiters got to their short period orbits, given that gas-giant planet building is supposed to take place beyond the ice-line at about 3 AU. Two major theories are generally used to explain this mystery. Firstly, exchange of energy and angular momentum between the newly-built planet and the progenitor dust and gas disk could result in planetary migration to a short period. This is generally believed to result in planets on circular orbits, with orbital angular momenta that are aligned with the host star spin. The competing theory which has gained more support in recent years, is that gravitational interactions leading to planet-planet scattering and/or Kozai interactions with massive and distant objects caused the planets to migrate violently (scattering) or slowly (Kozai) to short period, eccentric and misaligned orbits. These orbits are then expected to circularise and align under tidal interactions with the host star. In addition, the host star is expected to show evidence of spin-up if the tide on the star is strong enough. Our contribution to this field is to provide additional support for the scenario involving dynamical interaction and tidal damping. We present observational evidence in the form of 158 new radial velocity measurements for 12 planets and a reanalysis of existing radial velocity data and photometric constraints from the literature for a total of 64 planetary systems. We also critically consider a further 30 newly announced planets from the literature. We show that there is no evidence for a finite eccentricity in several cases that were previously claimed to be “exceptions” to the observed trend that close-in planets are on circular orbits and the generally accepted reason that they underwent strong tidal interactions. We also show that the dissipative effect of tides raised in the planet by the star and vice versa explain all the eccentricity and spin-orbit alignment measurements available for transiting planets. We find evidence for excess rotation of the star in 6 systems, showing that heavy and close-in objects can exert strong tidal effects on the star. Hot Jupiters on circular orbits clump on the mass-period relation, which thus appears to be related to the stopping mechanism of orbital migration for hot Jupiters

The prevalence of dust on the exoplanet HD 189733b from Hubble and Spitzer observations

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.The hot Jupiter HD 189733b is the most extensively observed exoplanet. Its atmosphere has been detected and characterized in transmission and eclipse spectroscopy, and its phase curve measured at several wavelengths. This paper brings together the results of our campaign to obtain the complete transmission spectrum of the atmosphere of this planet from UV to infrared with the Hubble Space Telescope, using the STIS, ACS and WFC3 instruments. We provide a new tabulation of the transmission spectrum across the entire visible and infrared range. The radius ratio in each wavelength band was re-derived, where necessary, to ensure a consistent treatment of the bulk transit parameters and stellar limb darkening. Special care was taken to correct for, and derive realistic estimates of the uncertainties due to, both occulted and unocculted star spots. The combined spectrum is very different from the predictions of cloud-free models for hot Jupiters: it is dominated by Rayleigh scattering over the whole visible and near-infrared range, the only detected features being narrow sodium and potassium lines. We interpret this as the signature of a haze of condensate grains extending over at least five scaleheights. We show that a dust-dominated atmosphere could also explain several puzzling features of the emission spectrum and phase curves, including the large amplitude of the phase curve at 3.6 μm, the small hotspot longitude shift and the hot mid-infrared emission spectrum. We discuss possible compositions and derive some first-order estimates for the properties of the putative condensate haze/clouds. We finish by speculating that the dichotomy between the two observationally defined classes of hot Jupiter atmospheres, of which HD 189733b and HD 209458b are the prototypes, might not be whether they possess a temperature inversion, but whether they are clear or dusty. We also consider the possibility of a continuum of cloud properties between hot Jupiters, young Jupiters and L-type brown dwarfs.Science and Technology Facilities Council (STFC)NASANSFTennessee State UniversityState of Tennesse