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K.S. de Boer

By B. P. Wakker, P. M. W. Kalberla, H. Van Woerden and M. E. Putman


We show 21-cm line profiles in the direction of stars and extragalactic objects, lying projected on highand intermediate-velocity clouds (HVCs and IVCs). About half of these are from new data obtained with the Effelsberg 100-m telescope, about a quarter are extracted from the Leiden-Dwingeloo Survey (LDS) and the remaining quarter were observed with other single-dish telescopes. H I column densities were determined for each HVC/IVC. Wakker (2001) (Paper I) uses these in combination with optical and ultraviolet high-resolution measurements to derive abundances. Here, an analysis is given of the difference and ratio of N(H I) as observed with a 9 ′ versus a 35 ′ beam. For HVCs and IVCs the ratio N(H I-9 ′)/N(H I-35 ′ ) lies in the range 0.2−2.5. For low-velocity gas this ratio ranges from 0.75 to 1.3 (the observed ratio is 0.85−1.4, but it appears that the correction for stray radiation is slightly off). The smaller range for the low-velocity gas may be caused by confusion in the line of sight, so that a low ratio in one component can be compensated by a high ratio in another − for 11 low-velocity clouds fit by one component the distribution of ratios has a larger dispersion. Comparison with higher angular resolution data is possible for sixteen sightlines. Eight sightlines with H I data at 1 ′ −2 ′ resolution show a range of 0.75−1.25 for N(H I-2 ′)/N(H I-9 ′), while in eight other sightlines N(H I-Lyα)/N(H I-9 ′ ) ranges from 0.74 to 0.98

Year: 2008
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