Unformatted text preview: subscript B denotes case B, the assumption of an optically thick nebula. Since, for example, the Hβ luminosity is we have in numbers of photons N (Hβ) = N(ion) α eff β / α B . which gives a fixed ratio between line and continuum intensities. For a given continuum shape, this gives a fixed (distance-independent) equivalent width (with respect to the ionizing continuum's optical tail) (Shuder 1981 ApJ 244, 12; Yee 1980 ApJ 241, 894). Similar arguments may be applied for He II emission, and for a few high-ionization forbidden lines like [Fe XIV] that require lots of far-UV to be produced....
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- Fall '10
- Astronomy, Planetary nebula, Lyman continuum