C$_{60}$ in Reflection Nebulae
  The fullerene C$_{60}$ has four infrared-active vibrational transitions at
7.0, 8.5, 17.4 and 18.9 $\mu$m. We have previously observed emission features
at 17.4 and 18.9 $\mu$m in the reflection nebula NGC 7023 and demonstrated
spatial correlations suggestive of a common origin. We now confirm our earlier
identification of these features with C$_{60}$ by detecting a third emission
feature at 7.04 $\pm$ 0.05 $\mu$m in NGC 7023. We also report the detection of
these three C$_{60}$ features in the reflection nebula NGC 2023. Our
spectroscopic mapping of NGC 7023 shows that the 18.9 $\mu$m C$_{60}$ feature
peaks on the central star and that the 16.4 $\mu$m emission feature due to
polycyclic aromatic hydrocarbons peaks between the star and a nearby
photodissociation front. The observed features in NGC 7023 are consistent with
emission from UV-excited gas-phase C$_{60}$. We find that 0.1-0.6% of
interstellar carbon is in C$_{60}$; this abundance is consistent with those
from previous upper limits and possible fullerene detections in the
interstellar medium. This is the first firm detection of neutral C$_{60}$ in
the interstellar medium.
