Computer Science
Scientific paper
Jul 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000hst..prop.8650c&link_type=abstract
HST Proposal ID #8650
Computer Science
Hst Proposal Id #8650 Ism And Circumstellar Matter
Scientific paper
Neutral atoms from the interstellar medium {ISM} flow into the solar system producing a diffuse emission at 1216 Angstrom by resonant scattering of solar H Ly-alpha emission. This wind contains the velocity distribution of the local ISM, plus modifications by solar gravity, radiation pressure, and ionization near the Sun, and the Ly-alpha emission line profile reveals these velocity signatures. Compared with the He flow at 26kms, consistent with the local ISM cloud, the H velocity of 18-21kms suggests an additional alteration of the H atom velocity distribution by charge exchange at the heliospheric interface. In cycles 1 and 4 we obtained initial GHRS echelle A Ly-alpha line profiles in 3 look directions. For cycle 9 we propose three focussed observations, taking higher sensitivity STIS echelle spectra to address the following key questions about the interplanetary H: 1} we will accurately measure the ratio of solar gravity to radiation pressure on the flow, 2} we will obtain upwind spectra close in time to FUSE spectra of the optically thin Ly-beta emission to directly measure the optical depth, and 3} we will obtain high S/N line profiles upwind to determine the extent of slowing of the inflow velocity distribution indicated in earlier HST and SOHO observations. The end goals of this program are to characterize the properties of the local ISM and its modification at the heliospheric interface.
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