Ca ii K interstellar observations towards early-type disc and halo stars, abundances and distances of intermediate- and high-velocity clouds.

We present Ca ii interstellar observations towards 20 early-type stars, to place lower distance limits to intermediate- and high-velocity clouds (IHVCs) in their lines of sight. The spectra are also employed to estimate the Ca abundance in the low-velocity gas towards these objects, when combined with Leiden–Dwingeloo 21-cm H i survey data of spatial resolution . Nine of the stars, which lie towards IHVC complexes H, K and gp, were observed with the intermediate dispersion spectrograph on the Isaac Newton Telescope at a resolution of 9000 (∼33 km s−1) and signal-to-noise ratio (S/N) per pixel of 75–140. A further nine objects were observed with the Utrecht Echelle Spectrograph on the William Herschel Telescope at and S/N per pixel of 10–25. Finally, two objects were observed in both Ca ii K and Na i D lines using the 2D COUDÉ spectrograph on the McDonald 2.7-m telescope at . The abundance of Ca ii plotted against H i column density for the objects in the current sample with heights above the Galactic plane ( z) exceeding 1000 pc is found to obey the Wakker & Mathis (2000) relation. Also, the reduced column density of Ca ii K as function of z is consistent with the larger sample taken from Smoker et al. (2003) . Higher S/N observations than those previously taken towards HVC complex H stars HD 13256 and HILT 190 reinforce the assertion that this lies at a distance exceeding 4000 pc. No obvious absorption is detected in observations of ALS 10407 and HD 357657 towards IVC complex gp. The latter star has a spectroscopically estimated distance of ∼2040 pc, although this was derived assuming the star lies on the main sequence and without any reddening correction being applied. Finally, no Ca ii K absorption is detected towards two stars along the line of sight to complex K, namely PG 1610+529 and PG 1710+490. The latter is at a distance of ∼700 pc, hence placing a lower distance limit to this complex, where previously only an upper distance limit of 6800 pc was available. [ABSTRACT FROM AUTHOR]