A new scheme of radiation transfer in HII regions including transient heating of grains

  • S. K. Ghosh
  • R. P. Verma


A new scheme of radiation transfer for understanding the infrared spectra of HII regions, has been developed. This scheme considers non-equilibrium processes (e.g. transient heating of the very small grains, VSG; and the polycyclic aromatic hydrocarbon, PAH) also, in addition to the equilibrium thermal emission from normal dust grains (BG). The spherically symmetric interstellar dust cloud is segmented into a large number of “onion skin” shells in order to implement the non-equilibrium processes. The scheme attempts to fit the observed SED originating from the dust component, by exploring the following parameters: (i) geometrical details of the dust cloud, (ii) PAH size and abundance, (iii) composition of normal grains (BG), (iv) radial distribution of all dust (BG, VSG & PAH).

The scheme has been applied to a set of five compact H II regions (IRAS 18116 − 1646, 18162 − 2048, 19442 + 2427, 22308 + 5812, and 18434 - 0242) whose spectra are available with adequate spectral resolution. The best fit models and inferences about the parameters for these sources are presented.

Key words

HII regions radiative transfer PAH VSG 


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Copyright information

© Indian Academy of Sciences 2000

Authors and Affiliations

  • S. K. Ghosh
    • 1
  • R. P. Verma
    • 1
  1. 1.Tata Institute of Fundamental ResearchMumbaiIndia

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