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Paper: Distances and Metallicities of High-Velocity Clouds
Volume: 165, The Third Stromlo Symposium: The Galactic Halo
Page: 469
Authors: van Woerden, Hugo; Peletier, Reynier F.; Schwarz, Ulrich J.; Wakker, Bart P.; Kalberla, Peter M. W.
Abstract: Distance and metallicity hold the key to our understanding of the physical properties and origins of HVCs. We review the results of determinations of distance and metallicity based on the presence or absence, and strength, of appropriate interstellar absorption lines in the spectra of halo stars at different distances and of extragalactic background sources. Upper or lower distance limits are available for several HVCs, and indicate various locations with respect to the major structural components of the Galaxy. The only distance bracket available, 2.5<z<7 kpc above the plane for Complex~A, places this HVC firmly in the Galactic Halo. Metallicity values of 0.1, 0.25 and 1.0 times solar, based on SII absorption and emission lines, have been measured for three HVCs. The wide ranges found for distance, location -- in Disk, Halo or beyond -- and metallicity suggest that both Galactic and extragalactic origins of HVCs are represented.
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