We present here observations of the auroral H Lyman alpha spectra obtained with the Goddard High Resolution Spectrograph onboard the Hubble Space Telescope performed from the June 24 to June 30, 1996. The spectra extend from 1214 A to 1220 A with a spectral resolution of 70 mA (Ech-A grating) using the Large Science Aperture (1.74 arcsec square). The pointing uncertainty is 1". Different nothern auroral regions have been mapped: the auroral arc where bright emissions are always observed (Long=146, Lat=+55N), the poleward region (emission inside the oval) at longitude=165 and latitude +65N. Two other spectra were taken when the nothern oval was just behind the limb (Long=25, Lat=+73N with Central Meridian Longitude=9.9 and 47.4). The intensities were found to be quite constant (6-7 kR). Using a model of energy deposition, we computed the vertical profile of the volume excitation rate of Lyman alpha produced by electron and proton precipitation. The transport of the resulting Lyman alpha photons through the atmosphere is quantitatively determined taking into account radiative transfer effects induced by the resonant scattering of these photons by the atmospheric H. Theoretical auroral Lyman alpha profiles are then compared to the observations. A spectrum has been taken at the Io footprint (Long=187, Lat=+51.5) and exhibits an aurora-like shape. This work was supported by NASA grants GO-3511.01 and NAGW-1766 to the University of Michigan.
AAS/Division for Planetary Sciences Meeting Abstracts #28
- Pub Date:
- September 1996