PUMPING UP THE [N I] NEBULAR LINES
- Department of Physics, University of Kentucky, Lexington, KY 40506 (United States)
- Centro de Radioastronomia y Astrofisica, UNAM Campus Morelia, Apartado Postal 3-72, 58090 Morelia, Michoacan (Mexico)
- Department of Physics and Astronomy, Vanderbilt University, Box 1807-B, Nashville, TN 37235 (United States)
- AWE plc, Aldermaston, Reading RG7 4PR (United Kingdom)
The optical [N I] doublet near 5200 A is anomalously strong in a variety of emission-line objects. We compute a detailed photoionization model and use it to show that pumping by far-ultraviolet (FUV) stellar radiation previously posited as a general explanation applies to the Orion Nebula (M42) and its companion M43; but, it is unlikely to explain planetary nebulae and supernova remnants. Our models establish that the observed nearly constant equivalent width of [N I] with respect to the dust-scattered stellar continuum depends primarily on three factors: the FUV to visual-band flux ratio of the stellar population, the optical properties of the dust, and the line broadening where the pumping occurs. In contrast, the intensity ratio [N I]/H{beta} depends primarily on the FUV to extreme-ultraviolet ratio, which varies strongly with the spectral type of the exciting star. This is consistent with the observed difference of a factor of five between M42 and M43, which are excited by an O7 and B0.5 star, respectively. We derive a non-thermal broadening of order 5 km s{sup -1} for the [N I] pumping zone and show that the broadening mechanism must be different from the large-scale turbulent motions that have been suggested to explain the line widths in this H II region. A mechanism is required that operates at scales of a few astronomical units, which may be driven by thermal instabilities of neutral gas in the range 1000-3000 K. In an Appendix A, we describe how collisional and radiative processes are treated in the detailed model N I atom now included in the CLOUDY plasma code.
- OSTI ID:
- 22092273
- Journal Information:
- Astrophysical Journal, Vol. 757, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
ASTRONOMY
ASTROPHYSICS
C CODES
COMPUTERIZED SIMULATION
COSMIC DUST
COSMIC PHOTONS
EMISSION SPECTRA
EXTREME ULTRAVIOLET RADIATION
FAR ULTRAVIOLET RADIATION
LINE BROADENING
LINE WIDTHS
OPTICAL PROPERTIES
PHOTOIONIZATION
PLANETARY NEBULAE
PLASMA
RADIANT HEAT TRANSFER
STARS
STELLAR RADIATION
SUPERNOVA REMNANTS