Advertisement

Interpretation of HII Region Radio Recombination Lines

  • C. M. Walmsley
Part of the Astrophysics and Space Science Library book series (ASSL, volume 80)

Abstract

There have been several recent reviews of the subject of radio recombination line from HII regions (Brown et al., 1978; Viner et al. 197 9) and I see no need for another review in the traditional sense. There does however seem to be a certain amount of confusion, at least among observers, as to whether or not theory and observations are consistent with one another. One problem is that simple models of the recombination line transfer do not appear to explain the observed run of line-to-continuumratio (TL/TC) with frequency. In fact, the observed values of TL/TC seem to vary only slightly from those which one would expect in the ideal situation of an optically thin L.T.E. gas without impact broadening. This has led some observers (see e.g. Chaisson and Dopita (1977)) to claim that, for practical purposes, L.T.E. may be assumed and electron temperatures derived on this basis. The claim is however hotly contested by Lockman and Brown (1978), who point out that there are difficulties fitting low frequency data (n >85) on the basis of an “L.T.E.” model. More fundamentally, it is clear that the lines are simply not in L.T.E. in the sense that, unless we completely misunderstand the physics of highly excited atoms in HII regions, the bn factors are not equal to unity and the line absorption coefficients are negative. Hence stimulated emission should occur and the question remains as to why its effects are not more apparent.

Keywords

Line Width Filling Factor Angular Resolution Emission Measure Excitation Parameter 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Brocklehurst, M. (1970) Mon. Not. Roy. Astron. Soc. 148, 417ADSGoogle Scholar
  2. Brocklehurst, M., Seaton, M.J. (1972) Mon. Not. Roy. Astron.Soc. 157, 179ADSGoogle Scholar
  3. Brown, R.L., Lockman, F.J., Knapp, G.R. (1978) Ann. Revs. Astron. Astrophys. 16, 445ADSCrossRefGoogle Scholar
  4. Chaisson, E.J., Dopita, M.A. (1977) Astron. Astrophys. 56, 385ADSGoogle Scholar
  5. Churchwell, E., Smith, L.F., Mathis, J., Mezger, P.G., Huchtmeier, W. (1978) Astron. Astrophys. 70, 719ADSGoogle Scholar
  6. Lockman, F.J., Brown, R.L. (1975) Astrophys. J. 201, 134ADSCrossRefGoogle Scholar
  7. Lockman, F.J., Brown, R.L. (1978) Astrophys. J. 222, 153ADSCrossRefGoogle Scholar
  8. McCall, M.L. (1979) Astrophys. J. 229, 962ADSCrossRefGoogle Scholar
  9. Pankonin, V., Walmsley, C.M., Harwit, M. (1979) Astron. Astrophys. 75, 34ADSGoogle Scholar
  10. Pankonin, V., Walmsley, C.M., Thum, C. (1980) Astron. Astrophys. (submitted)Google Scholar
  11. Pauls, T., Wilson, T.L. (1977) Astron. Astrophys. 60, L31ADSGoogle Scholar
  12. Pedlar, A. (1980) Submitted to Mon. Not. Roy. Astron. Soc.Google Scholar
  13. Shaver, P.A. (1979) Astron. Astrophys. 78, 116ADSGoogle Scholar
  14. Shaver, P.A. (1980) Astron. Astrophys. (in press)Google Scholar
  15. Simpson, J.P. (1973) Pub. Astron. Soc. Pacific 85, 479ADSCrossRefGoogle Scholar
  16. Thum, C., Mezger, P.G., Pankonin, V. (1980) Submitted to Astron. AstrophysGoogle Scholar
  17. Van Gorkom, J.H., Goss, W.M., Shaver, P.A., Schwarz, U.J. (1979) Astron. Astrophys. (submitted)Google Scholar
  18. Viner, M.R., Vallee, J.P., Hughes, V.A. (1979) Astrophys. J. Supplement 39, 405ADSCrossRefGoogle Scholar
  19. Wilson, T.L., Bieging, J., Wilson, W.E. (1979a) Astron. Astrophys. 71, 205ADSGoogle Scholar
  20. Wilson, T.L., Pauls, T.A., Ziurys, L.M. (1979b) Astron. Astrophys. 77, L3ADSGoogle Scholar

Copyright information

© D. Reidel Publishing Company 1980

Authors and Affiliations

  • C. M. Walmsley
    • 1
  1. 1.Max-Planck-Institut für RadioastronomieBonn 1Federal Republic of Germany

Personalised recommendations