Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...208.2002c&link_type=abstract
American Astronomical Society Meeting 208, #20.02; Bulletin of the American Astronomical Society, Vol. 38, p.101
Astronomy and Astrophysics
Astronomy
Scientific paper
This dissertation explores the consequences of atmospheric dynamics for observations of substellar mass objects (SMOs). We discuss first the growth of cloud particles of various compositions in brown dwarfs of different surface gravities and effective temperatures. We calculate the structure of these objects with a one-dimensional radiative transfer model. To determine particle sizes, we compare the timescales for microphysical growth processes, including nucleation, coagulation, and coalescence, to the timescale for gravitational sedimentation. We also allow for sustained uplifting of condensable vapor in convective regions. We show that particle sizes vary greatly over the range of objects studied. In most cases, we find that clouds on brown dwarfs do not dominate the opacity. Rather, they smooth the emergent spectrum and partially redistribute the radiative energy. We proceed then to discuss the meteorologies of extrasolar giant planets (EGPs). We present results from a three-dimensional model of atmospheric dynamics on the transiting Jupiter-like planet HD 209458b. As a close-in orbiter, HD 209458b is super-heated on its dayside. Tidal locking causes the dayside hemisphere to face the star in perpetuity, which leads to very different dynamics than is seen on Jupiter. The flow is characterized by an eastward supersonic jet (u 4 km/s) extending from the equator to the mid-latitudes. Temperature contrasts are 500 K at the photosphere. Winds blow the hottest regions downstream from the substellar point by 60 degrees, with direct implications for the infrared light curve. We then expand our simulations to study carbon chemistry in HD 209458b's atmosphere by coupling the CO/CH4 reaction kinetics to the dynamics. Disequilibrium results from slow reaction rates at low (p, T). We show how effective vertical quenching near the 3 bar level leads to uniformly high concentrations of CO at the photosphere, even in cool regions where CH4 is strongly favored thermodynamically.
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