A New 3.25 Micron Absorption Feature toward Monoceros R2/IRS 3

A new 3.2--3.5~$\mu$m spectrum of the protostar Mon~R2/IRS-3 confirms ourprevious tentative detection of a new absorption feature near 3.25 $\mu$m. Thefeature in our new spectrum has a central wavelength of 3.256 $\mu$m (3071cm$^{-1}$) and has a full-width at half maximum of 0.079 $\mu$m (75 cm$^{-1}$).We explore a possible identification with aromatic hydrocarbons at lowtemperatures, which absorb at a similar wavelength. If the feature is due toaromatics, the derived column density of C--H bonds is $\sim$1.8 $\times$$10^{18}$ cm$^{-2}$. If the absorbing aromatic molecules are of roughly thesame size as those responsible for aromatic emission features in theinterstellar medium, then we estimate that $\sim$9\% of the cosmic abundance ofcarbon along this line of sight would be in aromatic hydrocarbons, in agreementwith abundance estimates from emission features.Comment: 12 pages (26 kB), AASTex format. Also 1 Postscript figure (39 kB), tarred, compressed and uuencoded, added with 'figure' command. Postscript file or hardcopy available upon request to sellgren@payne.mps.ohio-state.edu. ApJL, in pres