New 3 Micron Spectra of Young Stellar Objects with H₂O Ice Bands

We present new ground-based 3 μm spectra of 14 young stellar objects with H₂O ice absorption bands. The broad absorption feature at 3.47 μm was detected toward all objects, and its optical depth is correlated with the optical depth of H₂O ice, strengthening an earlier finding. The broad absorption feature at 3.25 μm was detected toward two more sources, and an upper limit is given for a third source. The optical depths of the 3.25 μm feature obtained to date are better correlated with the optical depth of the refractory silicate dust than with that of H₂O ice. If this trend is confirmed, this would support our proposed identification of the feature as the C-H stretch of aromatic hydrocarbons at low temperature. An absorption feature at 3.53 μm due to solid methanol was detected for the first time toward Mon R2/IRS 2, as well as toward W33A and GL 2136. The wavelengths of the CH₃OH features toward W33A, GL 2136, and NGC 7538/IRS 9 can be fitted by CH₃OH-rich ices, whereas the wavelength of the feature toward Mon R2/IRS 2 suggests an H₂O-rich ice environment. Solid methanol abundances toward GL 2136, NGC 7538/IRS 9, and Mon R2/IRS 2 are 3%-5% relative to H₂O ice. There is an additional narrow absorption feature near 3.47 μm toward W33A. For the object W51/IRS 2, spatially resolved spectra from 2 to 4 μm indicate that the H₂O ice is located predominantly in front of the eastern component and that the H₂O ice extinction is much deeper than previously estimated. For the object RNO 91, spectra from 2 to 4 μm reveal stellar (or circumstellar) CO gas absorption and deeper H₂O ice extinction than previously estimated.