LOCAL CLOUD STRUCTURE FROM HST-GHRS

Echelle spectra at high resolution (lambda/Delta lambda = 90,000) of t he nearby stars alpha Aql (Altair), alpha Lyr (Vega), alpha Cen and de lta Cas, have been obtained with the Goddard High-Resolution Spectrogr aph (GHRS) on board the Hubble Space Telescope (HST), during the cycle s 1 and 3. In all but one spectra, interstellar Fe II and Mg II absorp tion lines are detected at the exact Doppler shifts expected for the L ocal Interstellar Cloud (LIC) velocity vector, providing new confirmat ions of this vector. These new results are combined with observations of alpha CMa (Sirius), alpha Aur (Capella), beta Pic, G191-B2B, alpha PsA (Fomalhaut) and beta Lee, also obtained with the GHRS. For these t argets too, absorption lines are detected at the expected LIC Doppler shift. ct Cen is exceptional, since its spectrum shows gas about 3 km s(-1) faster than the 26 km s(-1) velocity compatible with all other s tars, confirming that towards this direction a faster second cloud, or a faster extension of the LIC, is present in the immediate vicinity o f the Sun. From the measured LIC column-densities a first rough schema tic view of its contours in the galactic plane can be drawn. The dista nce to the cloud surface is estimated depending on the actual neutral H density. At least 7 (resp. 5) cloudlets, or masses of gas with diffe rent individual motions, do exist within a sphere of 12 (resp. 7) pc r adius (LIC included). We also provide upper limits on Vega and Altair circumstellar Fe II.