000002208 001__ 2208
000002208 005__ 20160701171701.0
000002208 0247_ $$2DOI$$a10.1088/0004-637X/757/1/79
000002208 037__ $$aASTROimport-365
000002208 100__ $$aFerland, G. J.
000002208 245__ $$aPumping up the [N I] Nebular Lines
000002208 260__ $$c2012
000002208 520__ $$aThe optical [N I] doublet near 5200 Å is anomalously strong in a variety of emission-line objects. We compute a detailed photoionization model and use it to show that pumping by far-ultraviolet (FUV) stellar radiation previously posited as a general explanation applies to the Orion Nebula (M42) and its companion M43; but, it is unlikely to explain planetary nebulae and supernova remnants. Our models establish that the observed nearly constant equivalent width of [N I] with respect to the dust-scattered stellar continuum depends primarily on three factors: the FUV to visual-band flux ratio of the stellar population, the optical properties of the dust, and the line broadening where the pumping occurs. In contrast, the intensity ratio [N I]/Hß depends primarily on the FUV to extreme-ultraviolet ratio, which varies strongly with the spectral type of the exciting star. This is consistent with the observed difference of a factor of five between M42 and M43, which are excited by an O7 and B0.5 star, respectively. We derive a non-thermal broadening of order 5 km s-1 for the [N I] pumping zone and show that the broadening mechanism must be different from the large-scale turbulent motions that have been suggested to explain the line widths in this H II region. A mechanism is required that operates at scales of a few astronomical units, which may be driven by thermal instabilities of neutral gas in the range 1000-3000 K. In an Appendix A, we describe how collisional and radiative processes are treated in the detailed model N I atom now included in the CLOUDY plasma code. 
000002208 700__ $$a Henney, W. J.
000002208 700__ $$a O'Dell, C. R.
000002208 700__ $$a Porter, R. L.
000002208 700__ $$a van Hoof, P. A. M.
000002208 700__ $$a Williams, R. J. R.
000002208 773__ $$c79$$i1$$pThe Astrophysical Journal$$v757$$y2012
000002208 85642 $$ahttp://esoads.eso.org/abs/2012ApJ...757...79F
000002208 905__ $$apublished in
000002208 980__ $$aREFERD