Published online by Cambridge University Press: 12 April 2016
This contribution reports results of recent absorption-line studies on La Palma and reviews earlier work done elsewhere. CaII has been found in absorption in five HVCs, mostly against extragalactic background sources. The CaII/HI ratios differ strongly, from 0.002 to 0.1 times solar, suggesting different origins of HVCs. Nondetections of CaII absorption in stellar spectra may provide lower limits to HVC distances, or be caused by small-scale structure or a low CaII/HI ratio in the HVC. Proper interpretation requires comparison of CaII/HI ratios in stellar and extragalactic probes, and use of high-resolution HI maps. No solid direct distance determinations of HVCs are available yet. The distance of Complex C is controversial.
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