Three Micron Hydrocarbon and Methanol Absorption in Taurus

The 3.3-4.0 μm spectral region contains the fundamental C-H stretching vibrations of alcohols and aliphatic hydrocarbons and provides a powerful method of characterizing the organic component of interstellar ices. Observations of sources in and behind the Taurus dark cloud are presented. We detect the 3.47 μm hydrocarbon feature toward Elias 16 (field star) and HL Tau (T Tauri star). Elias 16 provides the first detection of the 3.47 μm feature in the quiescent cloud medium. Our results are consistent with a location for the 3.47 μm absorber in the grain mantle material rather than the core. The 3.54 μm methanol (CH 3 OH) feature is not detected in any of the sources to a limit of τ 3.54 / A V < 0.0009, and CH 3 OH therefore has an abundance relative to H 2 O, which is likely to be less than 5%. This result sets limits on models for mantle evolution which involve processing of CH 3 OH-rich ices to form more complex organic species in regions of active star formation.