A FUSE Survey of Interstellar Molecular Hydrogen in Translucent Clouds

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dc.creatorRachford, Brian L.
dc.creatorSnow, Theodore P.
dc.creatorTumlinson, Jason
dc.creatorShull, J. Michael
dc.creatorBlair, William P.
dc.creatorFerlet, Roger
dc.creatorFriedman, Scott D.
dc.creatorGry, Cecile
dc.creatorJenkins, Edward B.
dc.creatorMorton, Donald C.
dc.creatorSavage, Blair D.
dc.creatorSonnentrucker, Paule
dc.creatorVidal-Madjar, Alfred
dc.creatorWelty, Daniel E.
dc.creatorYork, Donald G.
dc.date2002-05-23
dc.date.accessioned2026-07-07T10:31:16Z
dc.date.available2026-07-07T10:31:16Z
dc.descriptionWe report the first ensemble results from the FUSE survey of molecular hydrogen in lines of sight with A_V $\gtrsim$ 1 mag. We have developed techniques for fitting computed profiles to the low-J lines of H2, and thus determining column densities for J = 0 and J = 1, which contain $\gtrsim$99% of the total H2. From these column densities and ancillary data we have derived the total H2 column densities, hydrogen molecular fractions, and kinetic temperatures for 23 lines of sight. This is the first significant sample of molecular hydrogen column densities of 10^21 cm^-2, measured through UV absorption bands. We have also compiled a set of extinction data for these lines of sight, which sample a wide range of environments. We have searched for correlations of our H2-related quantities with previously published column densities of other molecules and extinction parameters. We find strong correlations between H2 and molecules such as CH, CN, and CO, in general agreement with predictions of chemical models. We also find the expected correlations between hydrogen molecular fraction and various density indicators such as kinetic temperature, CN abundance, the steepness of the far-UV extinction rise, and the width of the 2175A bump. Despite the relatively large molecular fractions, we do not see the values greater than 0.8 expected in translucent clouds. With the exception of a few lines of sight, we see little evidence for the presence of individual translucent clouds in our sample. We conclude that most of the lines of sight are actually composed of two or more diffuse clouds similar to those found toward targets like zeta Oph. We suggest a modification in terminology to distinguish between a "translucent line of sight" and a "translucent cloud."
dc.description64 pages in AASTeX preprint format, includes 12 figures and 11 tables; accepted for publication in ApJ
dc.identifierhttps://arxiv.org/abs/astro-ph/0205415
dc.identifierhttp://arxiv.org/abs/astro-ph/0205415
dc.identifierAstrophys.J.577:221-244,2002
dc.identifierdoi:10.1086/342146
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/178351
dc.subjectAstrophysics
dc.titleA FUSE Survey of Interstellar Molecular Hydrogen in Translucent Clouds
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