  Following our initial discovery of blue luminescence in the spectrum of the
Red Rectangle (RR) and its identification as fluorescence by small three- to
four-ringed polycyclic aromatic hydrocarbon (PAH) molecules, we report on the
spatial correlation between the blue luminescence and the 3.3 micron emission,
commonly attributed to small, neutral PAH molecules, and on the newly-derived
UV/optical attenuation curve for the central source of the RR, HD 44179. Both
results provide strong additional evidence for the presence of small PAH
molecules with masses of less than 250 a.m.u. in the RR, which supports the
attribution of the blue luminescence to fluorescence by the same molecules. We
contrast the excellent spatial correlation of the two former emissions with the
distinctly different spatial distribution of the extended red emission (ERE)
and of the dust-scattered light within the RR. The UV/optical attenuation curve
of the central star is unlike any interstellar extinction curve and is
interpreted as resulting from circumstellar opacity alone. Major contributions
to this opacity are absorptions in broad bands in the mid-UV, contributing to
the electronic excitation of the luminescing PAH molecules, and a sharp
ionization discontinuity near 7.5 eV in the far-UV, which places a sharp upper
limit on the masses of the PAH molecules that are responsible for this
absorption. The strength of the far-UV absorption leads to an abundance of the
PAH molecules of 10^{-5} relative to hydrogen in the RR. Such small PAHs are
perhaps unique to the environment in the RR, where they are shielded from harsh
radiation by the dense circmstellar disk.

Astrophysics