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

We present new groundbased 3 $\mu$m spectra of 14 young stellar objects withH_2O ice absorption bands. The broad absorption feature at 3.47 $\mu$m wasdetected toward all objects and its optical depth is correlated with theoptical depth of H_2O ice, strengthening an earlier finding. The broadabsorption feature at 3.25 $\mu$m was detected toward two more sources and anupper limit is given for a third source. The optical depths of the 3.25 $\mu$mfeature obtained to date are better correlated with the optical depth of therefractory silicate dust than with that of H_2O ice. If this trend isconfirmed, this would support our proposed identification of the feature as theC--H stretch of aromatic hydrocarbons at low temperature. An absorption featureat 3.53 $\mu$m due to solid methanol was detected for the first time towardMonR2/IRS2, as well as toward W33A and GL 2136. The wavelengths of the CH_3OHfeatures toward W33A, GL 2136, and NGC7538/IRS9 can be fit by CH_3OH-rich ices,while the wavelength of the feature toward MonR2/IRS2 suggests an H_2O-rich iceenvironment. Solid methanol abundances toward GL 2136, NGC7538/IRS9, andMonR2/IRS2 are 3-5 % relative to H_2O ice. There is an additional narrowabsorption feature near 3.47 $\mu$m toward W33A. For the object W51/IRS2,spatially resolved spectra from 2 to 4 $\mu$m indicate that the H_2O ice islocated predominantly in front of the eastern component and that the H_2O iceextinction is much deeper than previously estimated. For the object RNO 91,spectra from 2 to 4 $\mu$m reveal stellar (or circumstellar) CO gas absorptionand deeper H_2O ice extinction than previously estimated.Comment: 33 pages, 19 Postscript figures comprising Figures 1-11 in the text, to be published in Astrophysical Journa