New 3 micron spectra of young stellar objects with H2O ice bands.
BROOKE T.Y., SELLGREN K. and GEBALLE T.R.
Abstract (from CDS):
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.