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Spectra of Gaseous Nebulae

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

Abstract

In the 19th Century there raged an argument as to whether fuzzy telescopic objects loosely called nebulae were really stellar aggregates or a gas. Although he had resolved some diffuse objects as star clusters, Herschel, who was an astute observer, commented that the light of others appear so “soft” that it might arise from “a luminous fluid.”

Keywords

Central Star Planetary Nebula Optical Region Magnetic Dipole Transition Balmer Line 
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Some Suggested References

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  61. Early investigations of the Balmer decrement by Plaskett (1928), Carroll (1930), and Cillie (1932) culminated in the studies by: Menzel, D.H., and Baker, J.B. 1937, Ap. J., 86, 70ADSzbMATHGoogle Scholar
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  68. Whose results are very similar to those derived by W. Clarke (1965), which are described in Stars and Stellar Systems, 7, Nebulae and Interstellar Matter, 504, ed. B. Middlehurst and lT Aller, Chicago, Univ. of Chicago Press. See also: Gerola, H., and Panagia, N. 1968, Astrophys. Space Sci., 2, 285ADSGoogle Scholar
  69. Whose results are very similar to those derived by W. Clarke (1965), which are described in Stars and Stellar Systems, 7, Nebulae and Interstellar Matter, 504, ed. B. Middlehurst and lT Aller, Chicago, Univ. of Chicago Press. See also: Gerola, H., and Panagia, N. 1970, Astrophys. Space Sci., 8, 120.ADSGoogle Scholar
  70. Theoretical calculations for helium are given by: Brocklehurst, M. 1970, M.N.R.A.S., 157, 211.ADSGoogle Scholar
  71. Theoretical calculations for helium are given by: Robbins, R.R. 1968, Ap. J., 151, 497, 511ADSGoogle Scholar
  72. Theoretical calculations for helium are given by: Robbins, R.R. 1970, Ap. J., 160, 519.ADSGoogle Scholar
  73. Theoretical calculations for helium are given by: Robbins, R.R., and Bernat, A.P. 1974, Ap. J., 188, 309.ADSGoogle Scholar
  74. Balmer decrement measurements have been made by many observers. See, e.g.: Miller, J.S. 1971, Ap. J. Lett., 165. L101.ADSGoogle Scholar
  75. Balmer decrement measurements have been made by many observers. See, e.g.: Lee, P., et al. 1969, Ap. J., 155, 853.ADSGoogle Scholar
  76. The theory of continuous thermal radio-frequency radiation from H II regions and gaseous nebulae is given by many workers. Some representative papers are: Terzian, Y. 1974, Vistas in Astronomy, 16, 279.ADSGoogle Scholar
  77. The theory of continuous thermal radio-frequency radiation from H II regions and gaseous nebulae is given by many workers. Some representative papers are: Mezger, P., and Henderson, A.O. 1967, Ap. J., 147, 471.ADSGoogle Scholar
  78. The theory of continuous thermal radio-frequency radiation from H II regions and gaseous nebulae is given by many workers. Some representative papers are: Schraml, J., and Mezger, P.G. 1969, Ap. J., 156, 269.ADSGoogle Scholar
  79. The fundamental theory for formation of radio-frequency lines taking non-LTE effects into account was due to: Goldberg, L. 1966, Ap. J., 144, 1225ADSGoogle Scholar
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  87. Some illustrative applications to determinations of Te in Orion are given by: Pauls, T., and Wilson, T.L. 1977, Astron. Astrophys., 60, L31.ADSGoogle Scholar
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  89. Some illustrative applications to determinations of Te in Orion are given by: Lockman, F.J., and Brown, R.L. 1975, Ap. J., 201, 134.ADSGoogle Scholar
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  104. See I.A.U. Symposia No. 76 (1978) and No. 103 (1983), also see references in Appendix. A review article summarizing developments up to 1967: Czyzak, S.J. 1968, Nebulae and Interstellar Matter, ed. B. Middlehurst and L.H. Aller, Chicago, Univ. Chicago Press.Google Scholar
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  106. The literature is so extensive that we quote here only a few recent illustrative papers. Thus, for A-values: Mendoza, C, and Zeippen, C.J. 1982, M.N.R.A.S., 199. 1025.ADSGoogle Scholar
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  108. The literature is so extensive that we quote here only a few recent illustrative papers. Thus, for A-values: Eissner, W., and Zeippen, C.J. 1981, J. Phys. B., At. Mol. Phys., 14, 2125.ADSGoogle Scholar
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  114. Since forbidden line intensity ratios depend on both electron density and temperature, if we suppose that lines of two ionic species, e.g., O++ and N+, arise in the same strata, we can use the two sets of ratios to obtain Ne and Te (Aller and White 1949, A.J., 54, 181). This is the principle applied in diagnostic diagrams (Fig. 13). The method requires accurate Q-values, which were not available in 1949. Seaton’s breakthrough (see e.g., Proc. Roy. Soc. London, A218, 400, 1953; A231, 37, 1955; Phys. Soc. Proc, 68, 457, 1955), in cross section theory which enables reliable collision strengths to be computed, made it possible to determine trustworthy temperatures and densities from nebular line ratios.Google Scholar
  115. That forbidden line doublet ratios could depend on electron density was established by Aller, Ufford, and Van Vleck (1949) who measured the [0 II] 1(3727)/I(3726) ratio in a number of planetary nebulae and compared results with theoretical predictions. The observed intensity ratio was opposite to that predicted by the first-order theory. Improvements in the theory required taking into account the second-order spin-orbit interaction and magnetic interaction between the spin of one electron and the orbit of another! Even with these refinements all discordance was not removed. It was noted that the denser the nebula, the closer was the observed ratio to the predicted value. This variation was interpreted as a result of radiative and collisional processes that competed at different rates to populate and depopulate the 2d levels. Thus, the 3729/3726 ratio could provide a clue to the density. It was not until after Seaton had developed an adequate theory of collisional excitation that Seaton and Osterbrock (1967, Ap. J., 125, 66) were able to give a satisfactory treatment of the problem. Applications of np3 nebular line ratios of [S II], [a III], [Ar IV], and [K V] have been made by a number of workersGoogle Scholar
  116. See, e.g., Krueger et al., 1980, Proc. Nat’l. Acad. Sci. USA, 66, 14, 282Google Scholar
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  118. Saraph and Seaton, 1970, M.N.R.A.S., 148, 367.ADSGoogle Scholar
  119. With modern computers, we can easily solve equations of statistical equilibrium for five to typically fifteen levels using the best available atomic parameters (see, e.g., the compilation by Mendoza in I.A.U. Symposium No. 103).Google Scholar
  120. A useful compilation for forbidden lines of npq configurations of atoms and ions of C, N, O, Ne, Mg, Si, S, and Fe in the temperatore range between 5000 and 2,000,000 degrees has been given by M. Kafatos and J.P. Lynch (1980, Ap. J. Suppl., 42, 611).ADSGoogle Scholar
  121. 4.
    Evaluations of the accuracy of nebular line intensity predictions are difficult. Illustrative examples are given by Czyzak et al., 1980, Ap. J., 241, 719, for [Ar IV], and in Highlights of Astronomy, 1983, 4, 791, ed. R.M. West, Reidel Publ. Co. Much more work needs to be done on this problem.ADSGoogle Scholar
  122. 5.
    Observational Data Pertinent to Nebular Plasma Diagnostics Optical Region. A compilation of spectroscopic data on gaseous nebula up to 1975 is given by: Kaler, J.B. 1976, Ap. J. Suppl., 31, 517.ADSGoogle Scholar
  123. More recent data obtained by photoelectric photometry, image tube scanners, etc., include: Torres-Peimbert, S., and Peimbert, M. 1977, Rev. Mex. Astron. Astrofis., 2, 181.ADSGoogle Scholar
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  128. Ultraviolet Data for individual nebulae appear in many papers in contemporary periodicals. For a good starter see I.A.U. Symposium No. 103 and references therein, also: Universe at Ultraviolet Google Scholar
  129. Wavelengths, 1981, ed. R.D. Chapman, NASA Conference Publication No. 2171.Google Scholar
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  131. Infrared. For summaries and references for work on planetaries, see IAU Symposia No. 76, 1978; No. 103, 1983. See also: Aitken, D.K., and Roche, P.F. 1982, M.N.R.A.S., 200, 217.ADSGoogle Scholar
  132. Infrared. For summaries and references for work on planetaries, see IAU Symposia No. 76, 1978; No. 103, 1983. See also: Dinerstein, H. 1983, I.A.U. Symposium No. 103, 79.Google Scholar
  133. Infrared. For summaries and references for work on planetaries, see IAU Symposia No. 76, 1978; No. 103, 1983. See also: Zeilik, M. 1977, Ap. J., 218, 118 (H II regions)ADSGoogle Scholar
  134. Infrared. For summaries and references for work on planetaries, see IAU Symposia No. 76, 1978; No. 103, 1983. See also: Grasdalen, G. 1979, Ap. J., 229, 587.ADSGoogle Scholar
  135. Infrared. For summaries and references for work on planetaries, see IAU Symposia No. 76, 1978; No. 103, 1983. See also: Beck, S.C., Lacy, J.H., Townes, C.H., Aller, L.H., Geballe, T.R., and Baas, F. 1981, Ap. J., 249, 592.ADSGoogle Scholar
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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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