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Title: H I free-bound emission of planetary nebulae with large abundance discrepancies: Two-component models versus κ-distributed electrons

The 'abundance discrepancy' problem in the study of planetary nebulae (PNe), viz., the problem concerning systematically higher heavy-element abundances derived from optical recombination lines relative to those from collisionally excited lines, has been under discussion for decades, but no consensus on its solution has yet been reached. In this paper, we investigate the hydrogen free-bound emission near the Balmer jump region of four PNe that are among those with the largest abundance discrepancies, aiming to examine two recently proposed solutions to this problem: two-component models and κ electron energy distributions. We find that the Balmer jump intensities and the spectrum slopes cannot be simultaneously matched by the theoretical calculations based upon single Maxwell-Boltzmann electron-energy distributions, whereas the fitting can be equally improved by introducing κ electron energy distributions or an additional Maxwell-Boltzmann component. We show that although H I free-bound emission alone cannot distinguish between the two scenarios, it can provide important constraints on the electron energy distributions, especially for cold and low-κ plasmas.
Authors:
 [1] ; ;  [2]
  1. Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong (China)
  2. Department of Astronomy, Peking University, Beijing 100871 (China)
Publication Date:
OSTI Identifier:
22348308
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 780; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BOLTZMANN STATISTICS; COMPUTERIZED SIMULATION; ELECTRONS; ELEMENT ABUNDANCE; EMISSION; ENERGY SPECTRA; LIMITING VALUES; PLANETARY NEBULAE; PLASMA; RECOMBINATION