2008/09/22 by B. L. Rachford, Brian L. Rachford, Theodore P. Snow +21 · 226 citations
Chemistry · Physics and Astronomy · #Analytical Chemistry (journal) #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Chemistry #Chromatography #Extinction (optical mineralogy) #Galaxies: Formation, Evolution, Phenomena #Hydrogen #Hydrogen molecule #Optics #Physics #Sight #Stellar, planetary, and galactic studies #Ultraviolet #astro-ph
paper · pdf · doi:10.1088/0067-0049/180/1/125
published in The Astrophysical Journal Supplement Series 180(1), 125-137 (Institute of Physics) · 35 pages, 5 tables, 7 figures, accepted for publication in The Astrophysical Journal Supplements Series
arxiv created 2008/09/22 · openalex publication_date 2008/12/23 · openalex created_date 2016/06/24 · arxiv updated 2022/02/23 · openalex updated_date 2026/08/05
We report total abundances and related parameters for the full sample of the Far Ultraviolet Spectroscopic Explorer survey of molecular hydrogen in 38 translucent lines of sight. New results are presented for the "second half" of the survey involving 15 lines of sight to supplement data for the first 23 lines of sight already published. We assess the correlations between molecular hydrogen and various extinction parameters in the full sample, which covers a broader range of conditions than the initial sample. In particular, we are now able to confirm that many, but not all, lines of sight with shallow far-UV extinction curves and large values of the total-to-selective extinction ratio, R V = A V / E ( B − V )—characteristic of larger than average dust grains—are associated with particularly low hydrogen molecular fractions ( ). In the lines of sight with large R V , there is in fact a wide range in molecular fractions, despite the expectation that the larger grains should lead to less H 2 formation. However, we see specific evidence that the molecular fractions in this sub-sample are inversely related to the estimated strength of the UV radiation field and thus the latter factor is more important in this regime. We have provided an update to previous values of the gas-to-dust ratio, N (H tot )/ E ( B − V ), based on direct measurements of N (H 2 ) and N (H i ). Although our value is nearly identical to that found with Copernicus data, it extends the relationship by a factor of 2 in reddening. Finally, as the new lines of sight generally show low-to-moderate molecular fractions, we still find little evidence for single monolithic "translucent clouds" with .