DISTANCE AND METALLICITY LIMITS OF HIGH-VELOCITY CLOUDS

This paper presents results of a program to derive distances of high-v elocity clouds (HVCs) through measurement of absorption in the CaIIH a nd K lines. The problems of the method and their solutions are discuss ed in detail. A probable detection of absorption toward the Seyfert ga laxy Mark 106 is reported, which gives a Ca+ abundance of (17+/-6)x10( -9) in HVC complex A. The non-detection of CaII absorption against a s tellar probe sets a tentative lower limit of 1.6 kpc to the distance o f complex A. Non-detections of HVC CaII lines in 9 stars projected on complexes M, C and H may give distance limits, if the Ca+/HI ratio in those HVCs can be derived from absorptions against extra-galactic prob es. High-resolution HI observations are required to get reliable Ca+ a bundances. Westerbork HI synthesis observations are reported for sever al directions together with profiles obtained at the Effelsberg 100-me ter dish. From results on several HVCs, we conclude that the Ca+/HI ra tio may vary strongly between different HVC complexes.