DETECTION OF SPATIAL VARIATIONS IN THE (D H) RATIO IN THE LOCAL INTERSTELLAR-MEDIUM/

We present high resolution (Delta lambda similar or equal to 3.7km.s(- 1)) HT-GHRS observations of the DA white dwarf G191-B2B, and derive th e interstellar D/H ratio on the line of sight. We have observed and an alysed simultaneously the interstellar lines of H I, D I, N I, O I, Si II and Si III. We detect three absorbing clouds, and derive a total H I column density N(H I)=2.4 +/- 0.1 x 10(18)cm(-2), confirming our Cy cle 1 estimate, but in disagreement with other previous measurements. We derive an average D/H ratio over the three absorbing clouds N(D I)( total)/N(H I)(total)=1.12+/-0.08 x 10(-5), in disagreement with the pr eviously reported value of the local D/H as reported by Linsky et al. (1995) toward Capella. We re-analyze the GHRS data of the Capella line of sight, and confirm. their estimate, as we find (D/H)(Capella) = 1. 56 +/- 0.1 x 10(-5) in the Local Interstellar Cloud in which the solar system is embedded. This shows that the D/H ratio varies by at least similar to 30% within the local interstellar medium. Furthermore, the Local Interstellar Cloud is also detected toward G191-B2B, and we show that the D/H ratio in this component, toward G191-B2B, can be made co mpatible with that derived toward Capella. However, this comes at the expense of a much smaller value for the D/H ratio as averaged over the : other two components, of order 0.9 x 10(-5), and in such a way that the D/H ratio as averaged over all three components remains at the abo ve value, i.e. (D/H)(Total) = 1.12 X 10(-5). We thus conclude that, ei ther the D/H ratio varies from cloud to cloud, and/or the D/H ratio va ries within the Local Interstellar Cloud, in which the Sun is embedded , although our observations neither prove nor disprove this latter pos sibility.