We report the results of a re-analysis of KPNO-IRS spectroscopy of 30 locations in the prototypical WR shell nebula NGC 6888 (WN6 central star). The spectra covered a 3500–7200 Å wavelength range with R ≃ 360 effective spectral resolution. Electron temperatures for a majority of the locations were derived from the [N II] λλ(6548+6583)/5755 and the [O III] λλ(4959+5007)/4363 emission line ratios. T
e([N II]) ≃ 8000 ± 2400 K for eleven locations in the north and west parts of the shell and T
e([N II]) ≃ 13 000 ± 4000 K for five locations in the southwest part. By contrast, the [O III] temperatures show great variation with location, ranging from 12000 K to 55000 K, with the highest value being that for an [O III] filament located to the north and outside of the ensemble of knots defining the northern extent of the mass loaded ejecta from the star.
Using a combination of spectral ‘arithmetic’, shock- and photoionization models, we demonstrate that NGC 6888 is permeated by a strong hot wind-shocked gaseous medium (which extends outside the mass-loaded ejected material in the north and west) that contaminates the spectrum of any given location and must be removed to determine realistic T
e, and abundances for the ejected material in the observed knots. For some knots, the effects are such that the abundances obtained via naive empirical methods were found to be several times too small (particularly for O/H) than in reality. We present a few illustrative examples and discuss the implications the results have on abundances previously derived for NGC 6888, but more importantly, what these results imply about the origin of temperature fluctuations in other types of nebulae which may be influenced by stellar winds (i.e., planetary nebulae and H II regions).