2005/12/19 by Yangsen Yao, Q. Daniel Wang
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/500506
published as Astrophys.J.641:930-937,2006 · 9 pages, 4 figures and 3 tables, accepted for publication in ApJ 2006
arxiv created 2005/12/19 · openalex publication_date 2006/04/14 · arxiv updated 2009/12/01 · openalex created_date 2020/11/23 · openalex updated_date 2026/08/04
X-ray absorption spectroscopy provides a powerful tool in determining the metal abundances in various phases of the interstellar medium (ISM). We present a case study of the sight line toward 4U 1820-303, based on Chandra grating observations. The detection of O I, O II, O III, O VII, O VIII, and Ne IX Kα absorption lines allows us to measure the atomic column densities of the neutral, warm ionized, and hot phases of the ISM through much of the Galactic disk. By comparing these measurements with the 21 cm hydrogen emission and with the pulsar dispersion measure, we estimate the mean oxygen abundances in the neutral and total ionized phases as 0.3(0.2, 0.6) and 2.2(1.1, 3.5) in units of Anders & Greversse's solar value (90% confidence intervals). This significant oxygen abundance difference is apparently a result of molecule/dust grain destruction and recent metal enrichment in the warm ionized and hot phases. We also measure the column density of neon from its absorption edge and obtain a solar value of the Ne/O ratio accounting for the expected oxygen contained in molecules and dust grains. From a joint analysis of the O VII, O VIII, and Ne IX lines, we obtain the Ne/O abundance ratio of the hot phase as 1.4(0.9, 2.1) solar, which is not sensitive to the exact hot gas temperature distribution assumed. These comparable ISM Ne/O ratios for the different phases are thus considerably less than the value recently inferred from corona emission of solar-like stars.