We present new Spitzer IRS observations of HD 164270 ( WC9 , WR103 ) .
A quantitative analysis of the UV , optical , near- and mid-IR spectrum of HD 164270 is presented , allowing for line blanketing and wind clumping , revealing T _ { \ast } \sim 48kK , \log L / L _ { \odot } \sim 4.9 , \dot { M } \sim 10 ^ { -5 } M _ { \odot } yr ^ { -1 } for a volume filling factor of f \sim 0.1 .
Our models predict that He is partially recombined in the outer stellar wind , such that recent radio-derived mass-loss rates of WC9 stars have been underestimated .
We obtain C/He \sim 0.2 and O/He \sim 0.01 by number from optical diagnostics .
Mid-IR fine structure lines of [ Ne ii ] 12.8 \mu m and [ S iii ] 18.7 \mu m are observed , with [ Ne iii ] 15.5 \mu m and [ S iv ] 10.5 \mu m absent .
From these we obtain Ne/He \sim Ne ^ { + } /He = 2.2 \times 10 ^ { -3 } by number , 7 times higher than the Solar value ( as recently derived by Asplund et al .
) , and S/He \sim S ^ { 2 + } /He = 5.1 \times 10 ^ { -5 } by number .
From a comparison with similar results for other WC subtypes we conclude that WC9 stars are as chemically advanced as earlier subtypes .
We consider why late WC stars are exclusively observed in high metallicity environments .
In addition , we compare the UV/optical/mid-IR spectroscopic morphology of HD 164270 with the Planetary Nebula central star BD+30 3639 ( [ WC9 ] ) .
Their UV and optical signatures are remarkably similar , such that our quantitative comparisons confirm similarities in stellar temperature , wind densities and chemistry first proposed by Smith & Aller , in spite of completely different evolutionary histories , with HD 164270 presently a factor of ten more massive than BD+30 3639 .
At mid-IR wavelengths , the dust from the dense young , nebula of BD+30 3639 completely dominates its appearance , in contrast with HD 164270 .