A study of the dust distribution and extinction law in Mon R2

A. Natta, S. Beckwith, II. Evans N.J., S.C. Beck, A.F.M. Moorwood, E. Oliva

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The authors have observed infrared hydrogen recombination lines with a number of different beam sizes toward the H II region Mon R2 IRS 1. Two distinctly different models with variations in the extinction can fit the data: (i) If the variations are confined to scales comparable to or to larger than our smallest beam (~4"), the exponent in the extinction law (τ∝λ) must be 1.4±0.1, implying that grains have grown considerably larger in the dense cloud than in the diffuse interstellar medium. (ii) If the extinction varies on a much smaller scale (~0.3"), the authors can fit the data with β=1.85. The clumps must be quite small and dense [r (clump)~1.4×10-3 pc; M (clump)~6×10-4M; n(H2) (clump)~1.5×106 cm-3].
Original languageEnglish
Pages (from-to)143 - 8
JournalAstronomy and Astrophysics
Issue number1-2
StatePublished - Apr 1986


  • astronomical spectra
  • cosmic dust
  • H II region
  • hydrogen
  • infrared sources (astronomical)


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