The analysis of the H Lyman alpha emission line profile from Jupiter's aurora

We present the analysis and modeling of the emission spectra of the jovian northern auroral region taken from May 28 to June 3, 1993, with the Goddard High Resolution Spectrograph on board the Hubble Space Telescope. They ext end from 1204 to 1240 A covering H Lyman or and part of the Werner and the Lyman bands of H-2 We used the 2 x 2 arcsec large science aperture combined with the G160M grating (spectral resolution of 570 m Angstrom) centred on Jupiter's central meridian. The auroral region studied extends from 50 to 6 0 degrees north latitudes and from 130 to 220 degrees System III longitudes . Within the 1 arcsec pointing uncertainty, most of the region delineated b y the theoretical ovals at 5.9 and 30 jovian radii (R-J) in the VIP4 model of J. E. C. Connerney, M. H. Acuna, N. E Ness, and T. Satoh (1998, New mode ls of Jupiter's magnetic field constrained by the Io flux tube footprint. J . Geophys. Res. 103, 11,929-11,939), including the auroral oval derived fro m the Wide Field Planetary Camera 2 images by J. T. Clarke, G. E. Ballester , J. T. Trauger, R. Evans, J. E. P. Connerney, K. Stapelfeld, D. Crisp, P. I). Feldman, C. J. Burrows, S. Casertano, J. S. Gallagher, R. E. Griffiths, J. J. Hester, J. G, Hoessel, J. A. Holtzman, J. E. Krist, V, Meadows, J. R . Mould, PA, Scowen, A. M. Watson, and J. A, Westphal (1996, Far-ultraviole t imaging of Jupiter's aurora and the Io "footprint," Science 274, 404-409) , was sampled. We derive auroral brightnesses (averaged over the slit) rang ing from 20 kR in the 190-220 degrees longitude region to 30 kR in the 130- 160 degrees longitude range. We use the theoretical model developed by D. R ego, R. Prange, and L, Ben Jaffel (1999, Auroral Lyman alpha and H-2 bands from the giant planets. 3. Lyman Lu intensity and spectral profile includin g radiative effects and H-2 color ratios. J. Geophys. Res, Planets. 104, 59 39-5954), which calculates self-consistently the auroral Lyman or line prof ile for electron and proton precipitations and a given frequency redistribu tion function. This model shows that Lyman cr profiles are not dependent up on the identity of the particles for a given penetration depth. These profi les only constrain the atmospheric H column density above the emitting laye r, H-col. Best agreement with the data is found with the complete frequency redistribution (CR). We derive an auroral H-col of 1.3 x 10(16) cm(-2) for all spectra with an upper limit of 5 x 10(16) cm(-2). Precipitating proton s also produce fast H atoms by charge exchange which can also be excited, b ut the resulting Doppler-shifted profile was not detected, Present data thu s rule out protons as being the only precipitating particles. In the auroral zones, theoretical models predict that chemical reactions in duced by particle precipitations often result in the production of atomic h ydrogen, and thus an enhancement of the H density expected. However, the va lue of H-col we derive, between similar to8 and 23 times less than the equa torial values of L. Ben Jaffel, J. T. Clarke, Ii. Prange, Ii. Gladstone, an d A. Vidal-Madjar (1993, The Lyman alpha bulge of Jupiter: Effects of a non -thermal velocity field. J, Geophys, Res. Lett, 20(8), 747-750), is in good agreement with the auroral values of R. Prange, D, Rego, L. Pallier, L, Be n Jaffel, C, Emerich, J. T. Clarke, G. E. Ballester, and J. Ajello (1997, D etection of self-reversed Lyman alpha lines from the jovian aurorae with th e Hubble space Telescope, Astrophys. J. 484, L169-L173), This suggests that the H abundance predicted with standard atmospheric model is unrealistical ly large in the auroral region. (C) 2001 Academic Press.