THE VELOCITY STRUCTURE OF THE LOCAL INTERSTELLAR-MEDIUM PROBED BY ULTRA-HIGH-RESOLUTION SPECTROSCOPY

We present ultra-high-resolution (0.35 km s(-1) FWHM) observations of the interstellar Ca K line towards eight nearby stars (six of which ar e closer than 30 pc). The spectral resolution is sufficient to resolve the line profiles fully, thereby enabling us to detect hitherto unres olved velocity components, and to obtain accurate measurements of the velocity dispersions (b-values). Absorption components due to the Loca l Interstellar Cloud (LIC) and/or the closely associated 'G Cloud' are identified towards all but one star (gamma Oph), but only in one case (51 Oph) are both clouds reliably detected towards the same star. Mos t of these nearby clouds have velocity dispersions (b approximate to 2 km s(-1)) which suggest physical conditions similar to those inferred for the LIC (T-k approximate to 7000 K, v(t) approximate to 1 km s(-1 )), although at least three lines of sight (towards gamma Aqr, beta Ce n and beta Cen) also sample cooler and/or less turbulent material. The spectrum of the nearby Vega-excess star 51 Oph is of particular inter est, owing to evidence that several of the absorption components arise in the circumstellar environment.