Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21932605t&link_type=abstract
American Astronomical Society, AAS Meeting #219, #326.05
Astronomy and Astrophysics
Astronomy
Scientific paper
Gas giant exoplanets in tight orbits about their parent stars ("hot Jupiters") are in extreme environments not experienced by any solar system planet. Hot Jupiter upper atmospheres are intensely heated and some are observed to nearly fill their Roche Lobe, leading to suggestions that these planets are losing mass in an outflow.
However, the high ionization levels expected in the upper atmosphere imply that any outflow would be well-coupled to the planetary magnetic field, which may play a non-negligible role in the gas dynamics. We have constructed the first models of the upper atmosphere that include the effects of the intrinsic planetary magnetic field, as well as the stellar tide. The solutions exhibit the following three features: (1) a region near the equator of static, magnetically-confined gas, (2) a transonic outflow at mid-latitudes in a magnetically-channeled wind zone, and (3) a region near the poles where outflow can be quenched by a sufficiently strong stellar tide.
This MHD wind model provides a self-consistent calculation of the density/velocity structure of the upper atmosphere and mass/angular momentum loss rates, which are not well constrained by observations. Lyman-alpha transmission spectra computed from simulations and comparisons with the observed data have provided constraints on the atmospheric structure. One qualitative result of our work is that the observed Lyman-alpha absorption at several planetary radii may not directly constrain the mass loss rate, since the absorption is mainly due to gas confined in the planet's magnetosphere, rather than gas participating in an outflow.
Arras Phil
Li Zaidong
Trammell George B.
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