Search for Polycyclic Aromatic Hydrocarbons in the Outflows from
  Dust-Producing Wolf-Rayet Stars
  A combined mid-IR spectrum of five colliding-wind, massive, dust-producing
Population I Wolf-Rayet (WR) binaries shows a wealth of absorption and emission
details coming from the circumstellar dust envelopes, as well as from the
interstellar medium. The prominent absorption features may arise from a mix of
interstellar carbonaceous grains formed in high- (e.g., 3.4, 6.8, 7.2 $\mu$m)
and low-temperature (3.3, 6.9, 9.3 $\mu$m) environments. The broad emission
complexes around $\sim$6.5, 8.0 and 8.8 $\mu$m could arise from ionized, small
polycyclic aromatic hydrocarbon (PAH) clusters and/or amorphous carbonaceous
grains. As such these PAH emissions may represent the long sought after
precursors of amorphous Carbon dust. We also detect a strong $\sim$10.0 $\mu$m
emission in the spectra of WR48a and WR112, that we tentatively link to ionized
PAHs. Upon examining the available archival spectra of prodigious individual WR
dust sources, we notice a surprising lack of 7.7 $\mu$m PAH band in the
spectrum of the binary WR19, in contrast to the apparent strength of the 11.2,
12.7 and 16.4 $\mu$m PAH features. Strong PAH emissions are also detected in
the $\lambda>$10 $\mu$m spectrum of another dust-producing system, WR118,
pointing to the presence of large, neutral, presumably interstellar PAH
molecules towards WR19 and WR118.
