Computer Science
Scientific paper
Jul 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991hst..prop.2461l&link_type=abstract
HST Proposal ID #2461
Computer Science
Hst Proposal Id #2461
Scientific paper
We propose to use HST/HRS (R=10E5) in order to detect interstellar lines on some of the nearest stars: alpha Cen-A(1.3 pc), alpha CMa(2.7 pc), alpha Aql (5 pc), alpha Lyr (8.1 pc). Up to now, no optical lines have been detected towards those stars, except for alpha Aql (faint CaII, NaI absorptions). In the UV, lines can be found which are much stronger than in the visible, giving at high resolution the precise velocity and density structure of the nearby gas. The aim of this study is the determination of the characteristics of the parcel of ISM in which the sun is embedded (the "local" cloud): its heliocentric velocity vector (3 components), its temperature and state of ionization. Absorption lines to be observed are NI, OI,CI,SI,MgI,CII,FeII,SII,MgII,SiII, SIII,SiIII. These results will be compared to UV backscattered emissions of H and He in the solar system, which indicate V(H)=20 Km/s, T(H)=8000K, n(H)=.06at/cc and give precisely (within 3 degrees) the direction of the flow. If these characteristics are not compatible, it will bring constraints on the modifications of the neutral interstellar gas when penetrating the heliosphere. At present, nothing is known about the nature and the dimensions of the transition region between the interstellar and the solar plasma. HST/HRS will provide a unique opportunity to gather primary information on this interaction.
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