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Probing the Dark Secrets of PNe with ORLs

Published online by Cambridge University Press:  26 May 2016

X.-W. Liu
X.-W. Liu*
Affiliation:
Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK

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There are two long-standing problems in nebular astrophysics: a) The dichotomy of abundance determinations whereby heavy element abundances relative to hydrogen from collisionally excited lines (CELs) are systematically lower than those from (much fainter) optical recombination lines (ORLs), a discrepancy that can be traced back to Wyse (1942) and Aller & Menzel (1945) who pioneered the ORL method; and b) The dichotomy of temperature determinations whereby Te derived from the collisionally excited [O III] forbidden line ratio is systematically higher than that derived from Balmer jump of the H I recombination spectrum, a discrepancy first discovered by Peimbert (1971) and attributed to temperature fluctuations in the nebula (Peimbert 1967). Thanks to the rapid progress in detector technology and recombination theory for multi-electron systems, significant progress has been made in recent years in our understanding of these two fundamental problems, which could potentially affect the derivation of abundances for a wide range of photoionized nebulae, both galactic and extragalactic. Both types of dichotomy are found to be real and are most likely caused by astrophysical effects rather than uncertainties in observations or in the basic atomic physics. The two problems are shown to be related and can be explained by assuming that PNe contain a small mass of extremely cold (Te ~ 103 K) inclusions, highly enriched in helium and heavy elements, embedded in diffuse material of “normal” abundances (~ solar) and temperature (Te ~ 104 K). The existence and nature of such H-deficient inclusions in PNe remains a mystery. A recent review on this subject is given by Liu (2002).

Type
Part VI: The Ionized Gas in Planetary Nebulae
Information
Symposium - International Astronomical Union , Volume 209: Planetary Nebulae: Their Evolution and Role in the Universe , 2003 , pp. 339 - 346
Copyright
Copyright © Astronomical Society of the Pacific 2003 

References

Aller, L. H., Menzel, D. H. 1945, ApJ, 102, 239 Google Scholar
Czyzak, S. J., & Aller, L. H. 1973, ApJ, 181, 817 CrossRefGoogle Scholar
Dinerstein, H. L., Lafon, C. P., & Garnett, D. R. 2000, in Asymmetric Planetary Nebulae II, ed. Kastner, J., et al. (San Francisco: ASP), 301 Google Scholar
Garnett, D. R., & Dinerstein, H. L. 2001a, Rev.Mex.Astron.Astrofis. Ser.de Conf., 10, 13 Google Scholar
Garnett, D. R., & Dinerstein, H. L. 2001b, ApJ, 558, 145 CrossRefGoogle Scholar
Gruenwald, R., & Viegas, S. M. 1995, A&A, 303, 535 Google Scholar
Grandi, S. A. 1976, ApJ, 206, 658 Google Scholar
Iben, I. Jr., Kaler, J. B., Truran, J. W., & Renzini, A. 1983, ApJ, 264, 605 Google Scholar
Jacoby, G. H., & Ford, H. C. 1983, ApJ, 266, 298 Google Scholar
Kaler, J. B. 1988, PASP, 100, 620 Google Scholar
Kingdon, J., & Ferland, G. J. 1995, ApJ, 450, 691 Google Scholar
Liu, X.-W. 1998, MNRAS, 295, 699 CrossRefGoogle Scholar
Liu, X.-W. 2002, Rev.Mex.Astron.Astrofis. Ser.de Conf., in press Google Scholar
Liu, X.-W., et al. 1999, in Chemical Evolution from Zero to High Redshift, ed. Walsh, J. R. & Rosa, M. (Berlin: Springer-Verlag), 39 CrossRefGoogle Scholar
Liu, X.-W., & Danziger, I. J. 1993, MNRAS, 263, 256 Google Scholar
Liu, X.-W., Barlow, M. J., Cohen, , et al. 2001a, MNRAS, 323, 343–361 CrossRefGoogle Scholar
Liu, X.-W., Luo, S.-G., Barlow, , et al. 2001b, MNRAS, 327, 141 CrossRefGoogle Scholar
Liu, X.-W., Storey, P.J., Barlow, M.J., & Clegg, R.E.S. 1995, MNRAS, 272, 369 Google Scholar
Liu, X.-W., Storey, P. J., Barlow, M. J., et al. 2000, MNRAS, 312, 585 Google Scholar
Luo, S.-G., Liu, X.-W., & Barlow, M. J. 2001, MNRAS, 326, 1049 Google Scholar
Lutz, J., Alves, D., Becker, A., et al. 1998, AAS, 192, 5309 Google Scholar
Mathis, J. S., & Liu, X.-W. 1999, ApJ, 521, 212 Google Scholar
Peimbert, M. 1967, ApJ, 150, 825 CrossRefGoogle Scholar
Peimbert, M. 1971, Bol. Obs. de Tonantzintla Y Tacubaya, 6, 29 Google Scholar
Péquignot, D., Amara, M., Liu, X.-W., et al. 2002, Rev.Mex.Astron.Astrofis. Ser.de Conf., in press Google Scholar
Rubin, R. H. 1989, ApJS, 69, 897 Google Scholar
Smits, D. P. 1996, MNRAS, 278, 683 Google Scholar
Torres-Peimbert, S., Peimbert, M., & Peña, M. 1990, A&A, 233, 540 Google Scholar
Viegas, S., & Clegg, R. E. S. 1994, MNRAS, 271, 993 CrossRefGoogle Scholar
Williams, R. E., Woolf, N. J., Hege, E. K., et al. 1978, ApJ, 224, 171 CrossRefGoogle Scholar
Wyse, A. B. 1942, ApJ, 95, 356 CrossRefGoogle Scholar