Comparative Absorption and Emission Abundance Analyses of Nebulae: Ion Emission Densities for IC 418

Williams, Robert E.; Jenkins, Edward B.; Baldwin, J. A.; Sharpee, B. D.

doi:10.1086/345915

Cited by 6 publications

(3 citation statements)

References 45 publications

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“…The astrophysical importance lies in the fact that there are large discrepancies in abundances of several nebular elements, including C, N, O, S, Fe, and Ni, derived from recombination lines, as opposed to collisionally excited lines [6][7][8]. The present study on O II is also aimed at a possible resolution of this outstanding problem.…”

Section: Introductionmentioning

confidence: 99%

Low-energy fine-structure resonances in photoionization of O ii

Nahar

Montenegro

Eissner³

et al. 2010

Phys. Rev. A

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Resonant features in low-energy photoionization cross sections are reported in coupled-channel calculations for O II including relativistic fine structure. The calculations reveal extensive near-threshold resonant structures in the small energy region between the fine structure levels of the ground state 2p 2 ( 3 P 0,1,2 ) of the residual ion O III. Although the resonances have not yet been observed, they are similar to other experimentally observed features. They are expected to significantly enhance the very-low-temperature dielectronic recombination rates, potentially leading to the resolution of an outstanding nebular abundances anomaly. Higher energy partial and total photoionization cross sections of the ground configuration levels 2p 3 ( 4 S o 3/2 , 2 D o 3/2,5/2 , 2 P o 1/2,3/2 ) are found to be in agreement with experimental measurements on synchrotron-based photon sources [1][2][3], thereby identifying the excited O III levels present in the ion beams. These are also the first results from a recently developed version of Breit-Pauli R-matrix (BPRM) codes, with inclusion of two-body magnetic interaction terms. The improved relativistic treatment could be important for other astrophysical applications and for more precise benchmarking of experimental measurements.

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Section: Introductionmentioning

confidence: 99%

Low-energy fine-structure resonances in photoionization of O ii

Nahar

Montenegro

Eissner³

et al. 2010

Phys. Rev. A

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“…A possible explanation is that neutral gas is plentifully abundant within the ionized regions. This conjecture was supported by Williams et al (2003), who compared absorption-and emission-line spectra of IC 418 and found evidence that absorbing gas may be present. If we enhance the [O i] emissivity in the inner regions by a factor of ∼1.5, an excellent match between the predicted profile and observed one is achieved, as shown the Fig.…”

Section: Emission Line Profiles Of Ic 418mentioning

confidence: 77%

Emission line profiles as a probe of physical conditions in planetary nebulae

Zhang

2008

A&A

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Aims. We present an analysis of physical conditions in planetary nebulae (PNe) in terms of collisionally-excited line (CEL) and optical-recombination line (ORL) profiles. We aim to investigate whether line profiles could be used to study the long-standing CEL/ORL abundance-discrepancy problem in nebular astrophysics. Methods. Using 1D photoionization models and their assumed velocity fields, we simulate the line profiles of various ionic species. We attempt to use our model to account for the observed CEL and ORL profiles. As a case study we present a detailed study of line profiles of the low-excitation planetary nebula (PN) IC 418.Results. Our results show that the profiles of classical temperature and density diagnostic lines, such as [O iii] λλ4363, 5007, [S ii] λλ6716, 6731, and [Ar iv] λλ4711, 4740, provide a powerful tool to study nebular temperature and density variations. The method enables the CEL/ORL abundance-discrepancy problem to be studied more rigorously than before. A pure photoionization model of a chemically-homogeneous nebula seems to explain the observed disagreements in the profiles for the [O iii] λ4363 and the λ5007 lines, but cannot account for the differences between the [O iii] CELs and the O ii ORLs. We also investigate the temperature and density variations in the velocity space of a sample of PNe, which are found to be insignificant.

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“…More work is still in progress along these lines by various groups like the IRON Project, the FERRUM Project at Lund University, and the group at the University of Queen's Belfast. At this point it is worth mentioning the work of Williams et al (2003) who compared the abundance ratio Fe + /Ni + in IC 418 as obtained from UV resonant absorption lines, Fe ii λ1260.5 and Ni ii λ1317.2, as opposed to the determination from optical forbidden lines in emission. They get a large discrepancy between Fe + /Ni + >25 from absorption lines and Fe + /Ni + =5 from emission lines.…”

Section: The Iron-peak Elementsmentioning

confidence: 99%

Atomic processes in planetary nebulae

Bautista

2006

IAU

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Abstract. Historically, Planetary Nebula research has been a ground for much development in atomic physics. In the last five years the combination of a generation of powerful observatories, the development of ever more sophisticated spectral modeling codes, and important efforts on mass production of high quality atomic data have led to important progress in our understanding of the atomic spectra of PNe. In this paper I review such progress, including identification of heavy species (beyond the iron peak elements), observations of hyperfine emission lines and analysis of isotopic abundances, fluorescent processes, and new techniques for diagnosing physical conditions based on recombination spectra. Finally I discuss the new trends on the research of atomic processes in PNe.

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Comparative Absorption and Emission Abundance Analyses of Nebulae: Ion Emission Densities for IC 418

Cited by 6 publications

References 45 publications

Low-energy fine-structure resonances in photoionization of O ii

Low-energy fine-structure resonances in photoionization of O ii

Emission line profiles as a probe of physical conditions in planetary nebulae

Atomic processes in planetary nebulae

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