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The remarkably high excitation planetary nebula GC 6537
L H Aller1, S Hung, W A Feibelman
1Physics and Astronomy Department, University of California, Los Angeles, CA 90095, USA.
Summary
High excitation planetary nebula NGC 6537 shows shock excitation is crucial due to high temperatures, challenging standard photoionization models. This study estimates its chemical composition using combined photoionization and shock considerations.
Area of Science:
- Astronomy and Astrophysics
- Stellar Evolution
- Nebular Physics
Background:
- NGC 6537 is a point-symmetric planetary nebula with high excitation and complex kinematics.
- Standard photoionization models struggle to explain the observed high temperatures in certain regions of NGC 6537.
Purpose of the Study:
- To investigate the excitation mechanisms and chemical composition of NGC 6537.
- To determine the role of shock excitation in addition to photoionization.
- To refine nebular diagnostic techniques for high-excitation objects.
Main Methods:
- High-resolution spectroscopy using the Hamilton echelle Spectrograph.
- Analysis of ultraviolet and near-ultraviolet data.
- Application of nebular diagnostics and comparison with photoionization models.
Main Results:
- Observed high electron temperatures in regions with highly ionized atoms ([NeIV], [NeV]) indicate significant shock excitation.
- Standard photoionization models are insufficient to fully explain the observed spectral properties.
- Electron temperature variations with ionization potential and density effects were analyzed.
Conclusions:
- Shock excitation plays a critical role in NGC 6537, alongside photoionization.
- The chemical composition was estimated by integrating both photoionization and shock excitation models.
- Nebular diagnostics provide a more comprehensive understanding of high-excitation planetary nebulae.
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