He I 2.06 micron emission from nebulae

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4 Scopus citations


The spectrum emitted by any astronomical plasma is sensitive to a variety of details, some of which may not be obviously important. This paper describes the sensitivity of the He I 2.06 μm line to the gas opacity at ionizing energies. The intensity of the line relative to a hydrogen line depends on the He +/H+ ratio, but also on the ratio of continuous to He I Lyα line opacity, since this determines whether the Lyα line can scatter often enough to be converted to the 2.06 μm line. The intensity of the infrared line relative to Hβ can change by factors of several depending on details of the radiative transfer of He I Lyα, the gas microturbulence, the dust-to-gas ratio, and the level of ionization.

Original languageEnglish
Pages (from-to)247-249
Number of pages3
JournalAstrophysical Journal
Issue number1 PART 1
StatePublished - Feb 10 1999


  • H II regions
  • ISM: abundances
  • Line: formation
  • Plasmas
  • Radiation mechanisms: thermal
  • Radiative transfer

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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