2001/02/08 by B. P. Wakker · 14 citations
Physics and Astronomy · #Angular diameter #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Halo #Line (geometry) #Range (aeronautics) #Solar mass #Stellar, planetary, and galactic studies #Table (database) #astro-ph
paper · pdf · doi:10.1086/321783
published as Astrophys.J.Suppl. 136 (2001) 463-536 · To appear in the "Astrophysical Journal Supplement"; 82 pages; figures 6, 9 and 10 are in color; degraded figures (astro-ph restriction) - ask for good versions
arxiv created 2001/02/08 · openalex publication_date 2001/10/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
A table is presented that summarizes published absorption line measurements for the high- and intermediate-velocity clouds (HVCs and IVCs). New values are derived for N (H I) in the direction of observed probes, in order to arrive at reliable abundances and abundance limits (the H I data are described in Paper II). Distances to stellar probes are revisited and calculated consistently, in order to derive distance brackets or limits for many of the clouds, taking care to properly interpret nondetections. The main conclusions are the following. (1) Absolute abundances have been measured using lines of S II, N I, and O I, with the following resulting values: ~0.1 solar for one HVC (complex C), ~0.3 solar for the Magellanic Stream, ~0.5 solar for a southern IVC, and ~solar for two northern IVCs (the IV Arch and LLIV Arch). Finally, approximate values in the range 0.5-2 solar are found for three more IVCs. (2) Depletion patterns in IVCs are like those in warm disk or halo gas. (3) Most distance limits are based on strong UV lines of C II, Si II, and Mg II, a few on Ca II. Distance limits for major HVCs are greater than 5 kpc, while distance brackets for several IVCs are in the range 0.5-2 kpc. (4) Mass limits for major IVCs are 0.5-8 × 10 5 M ☉ , but for major HVCs they are more than 10 6 M ☉ . (5) The Ca II/H I ratio varies by up to a factor 2-5 within a single cloud, somewhat more between clouds. (6) The Na I/H I ratio varies by a factor of more than 10 within a cloud, and even more between clouds. Thus, Ca II can be useful for determining both lower and upper distance limits, but Na I only yields upper limits.