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Spectra of Gaseous Nebulae

  • Chapter
Physics of Thermal Gaseous Nebulae

Part of the book series: Astrophysics and Space Science Library ((ASSL,volume 112))

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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.”

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Some Suggested References

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  4. A discussion of the helium problem with suitable bibliographical references may be found in: Osterbrock, D.E. “Astrophysics of Gaseous Nebulae,” 1974, San Francisco: W.H. Freeman Co., p. 25 (hereafter referred to as A.G.N.).

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  11. Our discussion of absorption and emission processes involving H is taken from D.H. Menzel, 1937, Ap. J., 85, 330. This and other papers of the Harvard series on physical processes in gaseous nebulae are reprinted in: Physical Processes in Ionized Plasmas, ed. D.H. Menzel (New York: Dover Publications, 1962, hereafter referred to as PPIP).

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  25. Calculations for individual cross sections have been given by many workers. A few examples of this work are: Pradhan, A.K. 1980, M.N.R.A.S., 190, 5P. (Ne II, Ne III, Ne IV)

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  26. Radiative recombination of complex atoms has been discussed by: Gould, R.J. 1978, Ap. J., 219, 250.

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  30. The cross sections given by these authors for dielectronic recombination appear to be systematically too small. Dielectronic Recombination. A general review with references to previous work is given by: Seaton, M.J., and Storey, P.G. Atomic Processes and Applications, ed. P.G. Burke and B.L. Moiseiwitsch (Amsterdam: North-Holland Publications, 1976, p. 134).

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  31. Most of the discussions have pertained to high temperatures as in the solar corona and high densities as in quasars where the effects become more complex. See, e.g.: Burgess, A. 1964, Ap. J., 139, 776. (Corona)

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  32. Most of the discussions have pertained to high temperatures as in the solar corona and high densities as in quasars where the effects become more complex. See, e.g.: Burgess, A., and Summers, H.P. 1969, Ap. J., 157, 1008.

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  33. Most of the discussions have pertained to high temperatures as in the solar corona and high densities as in quasars where the effects become more complex. See, e.g.: Davidson, K. 1975, Ap. J., 195, 285. (Quasars)

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  34. Dielectronic recombination rates appropriate to nebular temperatures and densities are discussed, for example, by: Jacobs, V.L., Davis, J., Rogerson, J.E., and Blaha, M. 1979, Ap. J., 230, 627.

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  35. Dielectronic recombination rates appropriate to nebular temperatures and densities are discussed, for example, by: Storey, P.J. 1981, M.N.R.A.S., 195, 27P. See also I.A.TJ. Symposium No. 103.

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  36. Dielectronic recombination rates appropriate to nebular temperatures and densities are discussed, for example, by: Nussbaumer, H., and Storey, P.J. 1983, Astron. Astrophys.

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  37. Charge Exchange. A brief summarizing account of the problems of charge exchange, with references to earlier work and timely warnings pertaining to inherent uncertainties in theoretical calculations, is given by: Dalgamo, A. Planetary Nebulae (ed. Y. Terzian, International Astronomical Union Symposium No. 76, Dordrecht, Reidel, 1978, p. 139).

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  38. The astrophysical importance of oxygen-hydrogen charge exchange reactions was noticed by: Chamberlain, J.W. 1956, Ap. J., 124. 390.

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  39. Its effect on nebular ionization structure was examined by: Williams, R.E. 1973, M.N.R.A.S., 164, 111.

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  42. The Zanstra method has been applied to planetary nebulae symbiotic stars, Be stars, and diffuse galactic nebulae. See: Zanstra, H. 1931, Zeits. f. Astrofis., 2, 1, 329, 1239.

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  44. A systematic formulation is given by: Harman, R.J., and Seaton, M.J. 1966, M.N.R.A.S., 132. 15.

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  45. A summary of the earlier work with descriptions of investigations by: Ambarzumian (1932), Stoy (1933), Wurm (1951), and others are given by: Aller, L.H., and Liller, W. 1968, Stars and Stellar Systems, 7, 546

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  46. A summary of the earlier work with descriptions of investigations by: Ambarzumian (1932), Stoy (1933), Wurm (1951), and others are given by: Aller, L.H., and Liller, W. 1968, Nebulae and Interstellar Matter, ed. by Barbara Middlehurst and L.H. Aller, Chicago, Univ. Chicago Press.

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  47. Modernized versions of the Stoy method are given by: Kaler, J.B. 1976, Ap. J., 210, 843.

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  48. Modernized versions of the Stoy method are given by: Preite-Martinez, A., and Pottasch, A.S. 1983, Astron. Astrophys., 126, 31.

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  49. The pioneering ultraviolet study (with the ANS satellite is): Pottasch, R., Wesselius, P.R., Wu, C.C., Fieten, H., and van Duinen, R.J. 1979, Astron. Astrophys., 62, 95,

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  50. see also: Pottasch, R. 1981, Astron. Astrophys., 94, L13.

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  51. see also: Pottasch, R. 1983, Planetary Nebulae, Dordrecht, Reidel Publ. Co.

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  52. see also: Méndez, R. et al. 1981, Astron. Astrophys., 101, 323.

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  53. Bowen proposed his fluorescent mechanism in: 1935, Ap. J., 81, 1. The earliest theoretical treatments by D.H. Menzel and L.H. Aller, 1941, Ap. J., 94, 436

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  54. T. Hatanaka, 1947, J. Astr. Geophys. Japan, 21, 1

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  55. W. Unno, 1955, Publ. Astr. Soc. Japan, 7, 81, were hampered by poor atomic and observational data.

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  56. The first accurate models were given by R.J. Weymann and R.E. Williams, 1969, Ap. J., 157, 1201

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  57. J.P. Harrington, 1972, Ap. J., 176. 127.

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  59. Replace earlier calculations by H. Nussbaumer, 1969, Astrophys. Lett., 4, 183. A. Dalgarno and A. Sternberg, 1982, Ap. J., discuss the role of charge exchange. The BFM may play a role in many astrophysical sources.

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  60. T. Kallman and R. McCray, 1980, Ap. J., 242, 615, discuss its possible importance in X-ray sources where much of the soft X-ray luminosity absorbed by the nebula appears as Lya (He II) which controls the ionization and temperature structure of the plasma until degraded. The BFM is expected to have a major effect on the fate of these He II photons.

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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, 70

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  62. 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. 1938, Ap. J., 88, 52.

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  63. Further contributions were made by: Seaton, M.J. 1959, M.N.R.A.S., 119, 90

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  64. Further contributions were made by: Seaton, M.J. 1964, M.N.R.A.S., 127, 177.

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  65. Further contributions were made by: Pengelly, R.M., and Seaton, M.J. 1964, M.N.R.A.S., 127, 145.

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  66. The standard theory of Balmer decrement for H and He II is that by: Brocklehurst, M. 1971, M.N.R.A.S., 153, 471.

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  67. 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: Brocklehurst, M., and Seaton, M.J. 1972, M.N.R.A.S., 157, 179.

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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, 285

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  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.

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  70. Theoretical calculations for helium are given by: Brocklehurst, M. 1970, M.N.R.A.S., 157, 211.

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  71. Theoretical calculations for helium are given by: Robbins, R.R. 1968, Ap. J., 151, 497, 511

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  72. Theoretical calculations for helium are given by: Robbins, R.R. 1970, Ap. J., 160, 519.

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  73. Theoretical calculations for helium are given by: Robbins, R.R., and Bernat, A.P. 1974, Ap. J., 188, 309.

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  74. Balmer decrement measurements have been made by many observers. See, e.g.: Miller, J.S. 1971, Ap. J. Lett., 165. L101.

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  75. Balmer decrement measurements have been made by many observers. See, e.g.: Lee, P., et al. 1969, Ap. J., 155, 853.

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  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.

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  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.

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  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.

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  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, 1225

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  80. See also general review by: Brown, R.L., Lockman, F.J., and Knapp, G.R. 1978, Ann. Rev. Astron. Astrophys., 16, 445.

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  81. Atomic physics processes relavant to the radio frequency region: Oster, L.F. 1961, Rev. Mod. Phys., 33, 525 (free-free processes).

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  82. Atomic physics processes relavant to the radio frequency region: Menzel, D.H. 1969, Ap. J. Suppl., 18, 221 (f-values for H).

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  83. Atomic physics processes relavant to the radio frequency region: Seaton, M.J. 1972, Comments on Atomic and Molecular Physics, 3, 107 (density broadening of r.f. lines).

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  84. Atomic physics processes relavant to the radio frequency region: Brocklehurst, M., and Leeman, S. 1971, Astrophys. Lett., 9, 35.

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  85. Some illustrative applications to determinations of Te in Orion are given by: Mills, B.Y., and Shaver, P. 1967, Australian Jl. Phys., 21, 95.

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  86. Some illustrative applications to determinations of Te in Orion are given by: Chaisson, E.J., and Dopita, M.A. 1977, Astron. Astrophys., 56, 385.

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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.

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  88. Some illustrative applications to determinations of Te in Orion are given by: Lockman, F.J., and Brown, R.L. 1976, Ap. J., 207, 336

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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.

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  90. The optical continuum of gaseous nebulae was investigated by a number of workers; the importance of the two-photon emission was first pointed out by: Spitzer, L., and Greenstein, J.L. 1951, Ap. J., 114, 407.

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  91. The basic reference on nebular optical continua is: Brown, R.L., and Mathews, W.G. 1970, Ap. J., 160, 939.

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  92. See also: Peach, G. 1967, Mem. R.A.S., 71, 13

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  93. See also: Cox, D.P., and Mathews, W.G. 1969, Ap. J., 155, 859

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  94. See also: Drake, S.A., and Ulrich, R.K., 1981, Ap. J., 248, 380.

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  95. An observational check on lines and continuum in NGC 7027 is given by: Miller, J.S., and Mathews, W.G. 1972, Ap. J., 172, 593.

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  96. The theory of the emission line spectrum of an optically thick nebula at moderate-to-high densities is discussed, e.g., by: Capriotti, E.R. 1965, Ap. J., 142, 1101.

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  97. The theory of the emission line spectrum of an optically thick nebula at moderate-to-high densities is discussed, e.g., by: Panagia, N., and Ranieri, M. 1973, Astron. Astrophys., 24, 219.

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  98. The theory of the emission line spectrum of an optically thick nebula at moderate-to-high densities is discussed, e.g., by: Ferland, G., and Netzer, H. 1979, Ap. J., 229, 274.

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  99. The theory of the emission line spectrum of an optically thick nebula at moderate-to-high densities is discussed, e.g., by: Mathews, W.G., Blumenthal, G.R., and Grandi, S.A. 1980, Ap. J., 235, 971.

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  100. The theory of the emission line spectrum of an optically thick nebula at moderate-to-high densities is discussed, e.g., by: Drake, S.A., and Ulrich, R.K. 1980, Ap. J. Suppl., 42, 351.

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  101. Collisional Excitation and Ionization Rates for H are given, e.g., by: Johnson, L.G. 1972, Ap. J., 174, 227

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  102. see also: Drake, S., and Ulrich, R.K. 1980, Ap. J. Suppl., 42, 351, and references therein cited.

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  103. A-Values and Collision Strengths 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, Stars and Stellar Systems, 7, 403

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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.

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  105. 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., 198. 127

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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.

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  107. The literature is so extensive that we quote here only a few recent illustrative papers. Thus, for A-values: Nussbaumer, H., and Rusca, C. 1979, Astron. Astrophys., 72. 129.

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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.

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  109. Ω-Values Krueger, T.K., Czyzak, S.J. 1970, Proc. R. Soc. London A, 318. 531.

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  110. Seaton, M.J. 1975, M.N.R.A.S., 170. 476.

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  113. Applications to Nebular Diagnostics Early determinations of Tε employing [O III] lines (p2 configuration) were made by Menzel, Aller and Hebb (1941) using Ω-values computed by Hebb and Menzel (1940), A-values from Pasternack (1940), and from Shortley et al. (1941), Although the absolute values of these Ω’s, which were obtained from an inadequate theory, were substantially in error, the ratios were much less inaccurate, such that electron temperatures found by this method were of the order of 10% lower than the best modern values. They sufficed to show that electron temperatures of gaseous nebulae were in the neighborhood of 10,000°K.

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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.

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  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 workers

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  116. See, e.g., Krueger et al., 1980, Proc. Nat’l. Acad. Sci. USA, 66, 14, 282

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  118. Saraph and Seaton, 1970, M.N.R.A.S., 148, 367.

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  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).

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  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).

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  121. 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.

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  122. 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.

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  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.

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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

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  1. University of California, Los Angeles, USA

    Lawrence H. Aller

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© 1984 D. Reidel Publishing Company, Dordrecht, Holland

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Aller, L.H. (1984). Spectra of Gaseous Nebulae. In: Physics of Thermal Gaseous Nebulae. Astrophysics and Space Science Library, vol 112. Springer, Dordrecht. https://doi.org/10.1007/978-94-010-9639-3_2

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  • DOI: https://doi.org/10.1007/978-94-010-9639-3_2

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