Astronomy and Astrophysics – Astrophysics
Scientific paper
2001-10-30
Astronomy and Astrophysics
Astrophysics
To be published in Astrophysical Journal, March 2002
Scientific paper
10.1086/338380
Surprisingly large column densities of H3+ have been detected using infrared absorption spectroscopy in seven diffuse cloud sightlines (Cygnus OB2 12, Cygnus OB2 5, HD 183143, HD 20041, WR 104, WR 118, and WR 121), demonstrating that H3+ is ubiquitous in the diffuse interstellar medium. Using the standard model of diffuse cloud chemistry, our H3+ column densities imply unreasonably long path lengths (~1 kpc) and low densities (~3 cm^-3). Complimentary millimeter-wave, infrared, and visible observations of related species suggest that the chemical model is incorrect and that the number density of H3+ must be increased by one to two orders of magnitude. Possible solutions include a reduced electron fraction, an enhanced rate of H2 ionization, and/or a smaller value of the H3+ dissociative recombination rate constant than implied by laboratory experiments.
Evans II Neal. J.
Geballe Thomas Ronald
Hinkle Kenneth H.
Kawaguchi Kentaro
McCall Benhamin J.
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