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Full-Text Articles in Physics
The Planetary Nebula A39: An Observational Benchmark For Numerical Modeling Of Photoionized Plasmas, George H. Jacoby, Gary J. Ferland, Kirk T. Korista
The Planetary Nebula A39: An Observational Benchmark For Numerical Modeling Of Photoionized Plasmas, George H. Jacoby, Gary J. Ferland, Kirk T. Korista
Physics and Astronomy Faculty Publications
Galactic nebulae are the main probes for the chemical evolution of the interstellar medium. Yet, recent observations have shown that chemical abundances determined from recombination and collisionally excited emission lines can differ by as much as an order of magnitude in some planetary nebulae (PNs). Many PNs have complex geometries and morphological evidence for interactions from stellar winds, and it is not clear to what extent winds, inhomogeneities, or shocked gas affect the observed spectrum. There currently is no full explanation for this discrepancy, which brings into question whether we understand the physical state of these low-density plasmas at all. …
Measurement And Interpretation Of Deuterium-Line Emission In The Orion Nebula, C. R. O'Dell, Gary J. Ferland, W. J. Henney
Measurement And Interpretation Of Deuterium-Line Emission In The Orion Nebula, C. R. O'Dell, Gary J. Ferland, W. J. Henney
Physics and Astronomy Faculty Publications
We present new observations of the deuterium and hydrogen Balmer lines in the Orion Nebula. There is a real variation in the deuterium-to-hydrogen line ratios across the nebula, being greatest in the emission from the largest proplyd (Orion 244-440). We also present the results of a detailed model for the emission of these lines, the hydrogen lines being the result of photoionization and recombination while the deuterium lines are produced by fluorescent excitation of the upper energy states by the far-UV radiation from θ1 Ori C. Comparison of the observations and predictions of the line intensities shows good agreement, …
Fractal Quasar Clouds, Mark Bottorff, Gary J. Ferland
Fractal Quasar Clouds, Mark Bottorff, Gary J. Ferland
Physics and Astronomy Faculty Publications
This paper examines whether a fractal cloud geometry can reproduce the emission-line spectra of active galactic nuclei (AGNs). The nature of the emitting clouds is unknown, but many current models invoke various types of magnetohydrodynamic confinement. Recent studies have argued that a fractal distribution of clouds, in which subsets of clouds occur in self-similar hierarchies, is a consequence of such confinement. Whatever the confinement mechanism, fractal cloud geometries are found in nature and may be present in AGNs too. We first outline how a fractal geometry can apply at the center of a luminous quasar. Scaling laws are derived that …