Dust and Related Phenomena in Gaseous Nebulae

  • Lawrence H. Aller
Part of the Astrophysics and Space Science Library book series (ASSL, volume 112)


The importance of dust in the interstellar medium has long been recognized. The Coal Sack and the Great Rift in the Milky Way are two manifestations most obvious to the unaided eye. Barnard’s classical photographs, for example, and much later surveys such as the Stromlo Atlas of the Southern Milky Way demonstrate the omnipresence of dust and the extremely irregular way in which it is distributed. The Bok globules and the dark lanes in the Trifid Nebula attest to association of dust with HII regions. The dust/gas ratio appears to be of the order of 0.01 by mass and reasonably constant from one part of the galaxy to another. Radio, infrared, and UV observations have disclosed dust in many planetary nebulae. In some of these nebulae, a large fraction of the less volatile metals may be tied up in these grains which play important roles in the interstellar medium. Since they lock away atoms of many heavy elements such as Fe and Ti, and also lighter ones such as C, O, and Si, many atoms which could play roles as coolants for the gas are not there. Accordingly, the energy balance of the interstellar medium is affected. Grains also serve as catalysts for molecule formation. The formation of H2 and other molecules on grain surfaces may be an important process.


Interstellar Medium Dust Cloud Central Star Planetary Nebula Magellanic Cloud 
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.


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Selected References

Interstellar Extinction

  1. The fundamental investigations were those of R.J, Trumpler (1930), Publ. Astron. Soc. Pac., 42. 214, 267; Lick Obs. Bull., 14, 154, in which he showed that Aλ increased as the wavelength decreased (but not as steeply as λ‒4 [Rayleigh law]). He also estimated a mean photographic (blue) region absorption of 0.67 mag/kpc. Subsequent investigations by Schalen, Greenstein, van de Hülst and many others attempted to define the character of the obscuring particles (see Vol. 7 of Stars and Stellar Systems, “Nebulae of Interstellar Matter,” 1968, ed. B. Middlehurst and L.H. Aller, Chicago, University of Chicago Press — especially articles by H.L. Johnson and M. Greenberg). An excellent bibliography with special emphasis on topics relevant to gaseous nebulae is given by D.E. Osterbrock in Astrophysics of Gaseous Nebulae. A comprehensive treatment of the subject may be found in:Google Scholar
  2. Spitzer, L. 1978, Physical Processes in Interstellar Medium, Chapters 7, 8, and 9. New York: Wiley.Google Scholar

A concise summary with extensive bibliography, and giving a definitive interstellar extinction law, is to be found in:

  1. Savage, B.D., and Mathis, J.S. 1979, Ann. Rev. Astron. Astrophys., 17, 73.ADSCrossRefGoogle Scholar

Our discussion employed a version of the extinction law given by:

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  2. Important recent references that emphasize the variation of the ultraviolet extinction within the galaxy are:Google Scholar
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Methods for estimating the extinction in gaseous nebulae are given in Table 1 and references therein. Additional examples are given by:

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The planetary NGC 7027 is a rich source of information for studies of dust and molecules and their effects on nebular structure. See:

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A review of work up to 1977 and appropriate references are given by:

  1. Rank, D.M. 1978, Planetary Nebulae (ed. Y. Terzian), p. 103, Reidel.Google Scholar
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Discussions pertaining to calculation and interpretation of infrared excess (IRE), including also the influence of dust on temperature determinations for central stars, are given by:

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  5. The Henyey-Greenstein scattering formula is given by them in Ap. J., 93. 70, 1941. It has been employed by many investigators.Google Scholar

The anomalous extinction in Abell 30 is described by:

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Scattering properties of dust in the Orion Nebula were assessed by:

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The gas-to-dust ratio in the interstellar medium has been the subject of many researches; we quote here results from:

  1. Bohlin, R.C., Savage, B.D., Drake, J.F. 1978, Ap. J., 224, 132.ADSCrossRefGoogle Scholar

For the particle size distribution law in the general interstellar medium, see, e.g.:

  1. Mathis, J.S., Rump, W., and Nordsieck, K.H. 1977, Ap. J., 217, 425.ADSCrossRefGoogle Scholar

Heavy element depletion in the interstellar medium, formation, destruction, and properties of dust grains are discussed in a series of papers in Annual Reviews of Astronomy and Astrophysics. In addition to the previously cited summary by Savage and Mathis, we mention:

  1. Aanestad, P.A., and Purcell, E.M. 1973, A.R.A.A., 11, 309.ADSGoogle Scholar
  2. Salpeter, E.E. 1977, A.R.A.A., 15, 267.ADSGoogle Scholar
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  4. Jura, M. 1980a, Ap. J., 235, 63; 1980b, Highlights of Astronomy, 5, (ed. A. Wayman), p. 293, Reidel.Google Scholar

Empirical relationships involving polarization and extinction properties of grains are given by:

  1. Serkowski, K., Mathewson, D.S., and Ford, V.L. 1975, Ap. J., 196, 261.ADSCrossRefGoogle Scholar

There is some evidence from the work of Code, Nandy, and their respective associates and from other investigators that the extinction law in the Magellanic clouds is different from that in the galaxy. See, e.g.:

  1. Koomneef, J., and Code, A.D. 1981, Ap. J., 247. 860.ADSCrossRefGoogle Scholar
  2. Dust in galaxies has been discussed by many workers, see, e.g., Jura, M., 1981, Ap. J., 243. 108.ADSCrossRefGoogle Scholar

Copyright information

© D. Reidel Publishing Company, Dordrecht, Holland 1984

Authors and Affiliations

  • Lawrence H. Aller
    • 1
  1. 1.University of CaliforniaLos AngelesUSA

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