The ISM Toward Nearby High-Velocity Stars: Accurate H Columns, D/h, and H Walls

Details The ISM Toward Nearby High-Velocity Stars: Accurate H Columns, D/h, and H Walls The ISM Toward Nearby High-Velocity Stars: Accurate H Columns, D/h, and H Walls

Jul 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996hst..prop.6617l&link_type=abstract

HST Proposal ID #6617

Computer Science

Hst Proposal Id #6617 Interstellar Medium

Scientific paper

Accurate measurements of the deuterium/hydrogen (D/H) ratio inlocal interstellar gas can provide a critical benchmark forestimates of the primordial D/H ratio, one of the majorconstraints on Big Bang cosmology, and credible measurementsof spatial variations in D/H can constrain Galactic chemicalevolution models. Our extensive modelling of H I and D Iabsorption in the Ly-alpha line toward nearby stars andcomparison with GHRS echelle spectra has shown that the D Icolumn density can be measured accurately, but that the H Icolumn is uncertain because the opacity is high and theintrinsic stellar emission line is not well known. An elegantsolution to this problem is to study the interstellarabsorption for lines of sight to NEARBY HIGH-VELOCITY stars.Large stellar radial velocities shift half of the stellaremission line away from the interstellar absorption. One canthen determine what H I column density produces an intrinsicstellar line profile centered on the stellar radial velocity.We propose to study 2 high radial velocity stars locatedwithin 6 pc to measure accurately: (1) the H I columndensities, (2) the mean value and possible variations in D/H,(3) trace the size, temperature, density, and turbulentvelocity of the local interstellar cloud (LIC) and the Gcloud, and (4) search for hot H I that theoretical modelspredict should be located at the interfaces between the ISMand solar/stellar winds. GHRS spectra of Alpha Cen and EpsilonIndi provide the first evidence for this hot H I.

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