The optical interstellar spectrum of kappa Vel (HD 81188) and a measurement of interstellar cloud turbulence

We present ultra-high resolution (R approximate to 10(6)) observations of l ines due to interstellar Na I D, Ca II K, KI and Ti II towards K Vel (HD 81 188). Five velocity components are identified in both Na I and Cart, and tw o in KI; an upper limit is recorded for Ti II. The very high spectral resol ution has enabled us to resolve fully the intrinsic interstellar line profi les, and thereby obtain reliable measurements of the velocity dispersion pa rameters (b-values) for all identified velocity components. By comparing th e observed b-values for Na I and KI, which differ in mass by almost a facto r of 2, it has been possible to derive the kinetic temperature (Tk) and lin e-of-sight rms turbulent velocity (v(t)) simultaneously for the two clouds identified in both elements. We obtain rigorous upper limits of 0.46 and 0. 33 km s(-1) for v(t) in these two clouds, which are definitely subsonic at the measured temperatures. The three-dimensional turbulent velocity (equiva lent to root 3 x v(t)) is also almost certainly subsonic for both component s, although it might just exceed the isothermal sound speed if the kinetic temperatures were close to the lower limits permitted by the line-profile a nalysis.