Spatially resolved detection of crystallized water ice in a T Tauri object

Aims. We search for frozen water and its processing around young stellar objects (YSOs of class I/II). We try to detect potential, regional differences in water ice evolution within YSOs, which is relevant to understanding the chemical structure of the progenitors of protoplanetary systems and the evolution of solid materials. Water plays an important role as a reaction bed for rich chemistry and is an indispensable requirement for life as known on Earth. Methods. We present our analysis of NAOS-CONICA/VLT spectroscopy of water ice at 3 μm for the T Tauri star YLW 16 A in the ρ Ophiuchi molecular cloud. We obtained spectra for different regions of the circumstellar environment. The observed absorption profiles are deconvolved with the mass extinction profiles of amorphous and crystallized ice measured in laboratory. We take into account both absorption and scattering by ice grains. Results. Water ice in YLW16A is detected with optical depths of between τ = 1.8 and τ = 2.5. The profiles that are measured can be fitted predominantly by the extinction profiles of small grains (0.1 μm–0.3 μm) with a small contribution from large grains (