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Full-Text Articles in Physical Sciences and Mathematics
Collisional Effects In He I: An Observational Analysis, J. B. Kingdon, Gary J. Ferland
Collisional Effects In He I: An Observational Analysis, J. B. Kingdon, Gary J. Ferland
Physics and Astronomy Faculty Publications
Accurate and reliable helium abundances can test modern theories of galactic and primordial nucleosynthesis. Unfortunately, there is some question whether current theory can account for collisional contributions to He I. We present new observations of two planetary nebulae (PNs) in the range λ850-λ9650, which we use to assess the importance of collisonal effects in the He I spectrum. The first object, NGC 7027, is expected to show relatively strong collisional enhancement, while the second, NGC 7026, should display only small effects. We derive new collision-to-recombination correction factors, based on new collision strengths from the 29-state quantal calculation …
Grains In Ionized Nebulae: Spectral Line Diagnostics, J. B. Kingdon, Gary J. Ferland, W. A. Feibelman
Grains In Ionized Nebulae: Spectral Line Diagnostics, J. B. Kingdon, Gary J. Ferland, W. A. Feibelman
Physics and Astronomy Faculty Publications
The depletion of condensable elements onto grains in gaseous nebulae can provide evidence that dust is well mixed with the ionized gas. Al and CA are two of the most depleted elements in the general interstellar medium, and it is therefore important to measure their abundances within the ionized region of nebulae. We compute a large grid of photoionization models and identify sets of line ratios which are relatively insensitive to stellar and nebular parameters, and are thus excellent diagnostics for determining relative abundances. Based on the absence of the [Ca II] λλ7291, 7324 doublet and the detection of …