Deviations from He I Case B Recombination Theory and Extinction Corrections in the Orion Nebula

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dc.creatorBlagrave, K. P. M.
dc.creatorMartin, P. G.
dc.creatorRubin, R. H.
dc.creatorDufour, R. J.
dc.creatorBaldwin, J. A.
dc.creatorHester, J. J.
dc.creatorWalter, D. K.
dc.date2006-10-20
dc.date.accessioned2026-07-07T10:40:34Z
dc.date.available2026-07-07T10:40:34Z
dc.descriptionWe are engaged in a comprehensive program to find reliable elemental abundances in and to probe the physical structure of the Orion Nebula, the brightest and best-resolved H II region. In the course of developing a robust extinction correction covering our optical and ultraviolet FOS and STIS observations, we examined the decrement within various series of He I lines. The decrements of the 2^3S-n^3P, 2^3P-n^3S and 3^3S-n^3P series are not in accord with caseB recombination theory. None of these anomalous He I decrements can be explained by extinction, indicating the presence of additional radiative transfer effects in He I lines ranging from the near-IR to the near-UV. CLOUDY photoionization equilibrium models including radiative transfer are developed to predict the observed He I decrements and the quantitative agreement is quite remarkable. Following from these results, select He I lines are combined with H I and [O II] lines and stellar extinction data to validate a new normalizable analytic expression for the wavelength dependence of the extinction. In so doing, the He+/H+ abundance is also derived.
dc.description42 pages, 10 figures. To be published in ApJ
dc.identifierhttps://arxiv.org/abs/astro-ph/0610621
dc.identifierhttp://arxiv.org/abs/astro-ph/0610621
dc.identifierAstrophys.J.655:299-315,2007
dc.identifierdoi:10.1086/510151
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/181373
dc.subjectAstrophysics
dc.titleDeviations from He I Case B Recombination Theory and Extinction Corrections in the Orion Nebula
dc.typetext

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