Astrophysics and Space Science

, Volume 34, Issue 1, pp 155–173 | Cite as

UV radiation fields in dark clouds

  • A. P. Whitworth
Article
Received:

Abstract

How dark is it inside a dark cloud? If—as is currently believed-interstellar extinction at UV wavelengths is mainly due to scattering with a strongly forward throwing phase-function, the interior of a dark cloud may be much better illuminated at UV wavelengths than its measured extinction would suggest. We consider the penetration of radiation into a dark cloud against scattering and absorption by grains; and we define a new group property for interstellar grains, the exclusion optical depth τd. τd is a measure of the ability of the grains to exclude radiation from the interior of an externally illuminated cloud. Radiation—as measured by the radiation energy density-penetrates the cloud approximately as if against pure absorption only, with effective optical depth τd. Thus τd is a conceptually and numerically useful quantity when estimating the role of UV radiation in the thermal and chemical balance within a dark cloud. Computations are made of the radiation fields in (1200, 4500) Å, at the centres of dark clouds with measured visual extinctions. It is found that even in very dark clouds, the radiation energy density in (1200, 1800) Å may be significant, due to the high grain albedo at these short wavelengths.

Keywords

Radiation Energy Density Short Wavelength Radiation Energy Radiation Field 
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.
This is a preview of subscription content, log in to check access.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Aannestad, P. A. and Purcell, E. M.: 1973,Ann. Rev. Astron. Astrophys. 11, 309.Google Scholar
  2. Abramowitz, M. and Stegun, I. A.: 1964,Handbook of Mathematical Functions, Dover, New York.Google Scholar
  3. Bless, R. C. and Savage, B. D.: 1972,Astrophys. J. 171, 293.Google Scholar
  4. Brown, R. L.: 1972,Astrophys. J. 173, 593.Google Scholar
  5. Carrasco, L., Strom, S. E., and Strom, K.M.: 1973,Astrophys. J. 182, 95.Google Scholar
  6. Herbst, E. and Klemperer, W.: 1973,Astrophys. J. 185, 505.Google Scholar
  7. Hollenbach, D. and Salpeter, E. E.: 1970,J. Chem. Phys. 53 79.Google Scholar
  8. Hoyle F. and Wickramasinghe, N. C.: 1967,Nature 214, 969.Google Scholar
  9. Mestel, L. and Spitzer, L., Jr.: 1956,Monthly Notices Roy. Astron. Soc. 116, 503.Google Scholar
  10. Solomon, P. M. and Klemperer, W.: 1972,Astrophys. J. 178, 389.Google Scholar
  11. Watson, W. D.: 1972,Astrophys. J. 176, 103.Google Scholar
  12. Watson, W. D. and Salpeter, E. E.: 1972a,Astrophys. J. 174, 321.Google Scholar
  13. Watson, W. D. and Salpeter, E. E.: 1972b,Astrophys. J. 175, 659.Google Scholar
  14. Werner, M. W. and Salpeter, E.E.: 1969,Monthly Notices Roy. Astron. Soc. 145, 249.Google Scholar
  15. Whitworth, A. P.: 1972, unpublished Ph.D. dissertation, Manchester.Google Scholar
  16. Wickramasinghe, N. C.: 1973,Light Scattering Functions for Small Particles, Hilger, London.Google Scholar
  17. Wickramasinghe, N. C. and Nandy, K.: 1972,Rep. Prog. Phys. 35, 157.Google Scholar
  18. Witt, A. N. and Johnson, M. W.: 1973,Astrophys. J. 181, 363.Google Scholar
  19. Witt, A. N. and Lillie, C. F.: 1973,Astron. Astrophys. 25, 397.Google Scholar

Copyright information

© D. Reidel Publishing Company 1975

Authors and Affiliations

  • A. P. Whitworth
    • 1
  1. 1.LeidenThe Netherlands

Personalised recommendations