HR: 0800h
AN: P11A-0094    [Abstracts]
TI: H Lyman-Alpha Disc Emission from the Upper atmosphere of Jupiter: New Radiation Transfer Diagnosis
AU: * Ben Jaffel, L
EM: bjaffel@iap.fr
AF: Institut d'Astrophysique de Paris-CNRS-UPMC, 98Bis Blvd Arago, Paris, 75014 France
AU: Clarke, J T
EM: jclarke@bu.edu
AF: Boston University-Department Astronomy, 725 Commonwealth Ave, Boston, MA 02215 United States
AB: The properties of the upper atmosphere of Jupiter have been of much interest with the still unresolved issue of the H Ly-alpha bulge, suprathermal hydrogen, and coronal Ly-alpha emissions as revealed by recent high-resolution observations made by the Hubble Space Telescope Imaging Spectrometer (STIS). To help understand these questions better, we have performed a theoretical study of Jupiter's upper atmosphere using its reflected solar Ly-alpha. This uses the adding-doubling radiation transfer method in which we take into account the curvature effect of the planetary atmosphere. Our goal is to test the sensitivity of the Jovian Ly-alpha emission line in relation to H column density, eddy diffusion coefficient, frequency redistribution function for photon scattering, the temperature vertical profile, and a hot atomic H layer embedded into the top of the atmosphere. Beyond reasserting finding of earlier studies, particularly the Ly-a center-to-limb (CTL) brightening, self-reversed line profile at disk center, and wide line profile on the planetary limb, we focus in this study on developing new diagnosis tools, to attain more confidently the unknown structure of Jupiter's thermosphere. First, using the brightness distribution for specific wavelength bands as proposed by Ben Jaffel et al., A&A, 204, 319, 1988, we show how to derive the thickness of the atomic H layer above the homopause level by a new technique that uses the spatial gap that separates the optical limb positions of respectively the line core and line wing. We also propose to derive the eddy diffusion coefficient at the homopause level, using the Q ratio between the limb peak brightness and the intensity from other regions over the planetary disc. This new technique only requires low-resolution observations and does not depend on the absolute calibration of the corresponding instrument. Finally, the relationship between the intensity of a specific wavelength range of the emission line and the temperature gradient in the thermosphere is demonstrated, allowing a new tool to access that fundamental property. Quick comparisons with some existing data show the strength of the proposed approach and opens new horizons to use strong resonant emission line at high resolution as a diagnostic for the state and structure of planetary upper atmospheres.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0350 Pressure, density, and temperature
DE: 0360 Radiation: transmission and scattering
DE: 6200 PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS
DE: 7549 Ultraviolet emissions
SC: Planetary Sciences [P]
MN: Fall Meeting 2005