2007/07/02 by Daniel E. Welty, D. E. Welty · 2 citations
Chemistry · Physics and Astronomy · #Absorption (acoustics) #Absorption spectroscopy #Analytical Chemistry (journal) #Astro and Planetary Science #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Atomic physics #Chemistry #Excited state #Optics #Physics #Spectral line #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/521269
33 pages, 6 figures, aastex, accepted to ApJ
arxiv created 2007/07/02 · openalex publication_date 2007/10/19 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We discuss the results of continued optical and UV spectroscopic monitoring of the variable intermediate-velocity (IV) absorption at v ☉ = -38 km s -1 toward HD 219188. After reaching maxima in mid-2000, the column densities of both Na I and Ca II in that IV component declined by factors ≳2 by the end of 2006. Comparisons between echelle spectra from HST STIS (2001, 2003, 2004) and HST GHRS (1994-1995) indicate the following: (1) The absorption from the dominant species S II, O I, Si II, and Fe II is roughly constant for all four epochs—suggesting that the total N (H) (~6 × 10 17 cm -2 ) and the (mild) depletions did not change significantly over a period of nearly 10 years. (2) The column densities of the trace species C I (both ground and excited fine-structure states) and of the excited state C II* all increased by factors of 2-5 between 1995 and 2001—implying increases in the hydrogen density n H (from about 20 cm -3 to about 45 cm -3 ) and in the electron density n e (by a factor ≳3) over that 6 yr period. (3) The column densities of C I and C II*—and the corresponding inferred n H and n e —then decreased slightly between 2001 and 2004. (4) The changes in C I and C II* are very similar to those seen for Na I and Ca II. The relatively low total N (H) and the modest n H suggest that the -38 km s -1 cloud toward HD 219188 is not a very dense knot or filament. Partial ionization of hydrogen appears to be responsible for the enhanced abundances of Na I, C I, Ca II, and C II*. In this case, the variations in those species reflect differences in density and ionization [and not N (H)] over scales of tens of AU.