Water and methanol ice in L 1544

Abstract

Context. Methanol and complex organic molecules have been found in cold starless cores, where a standard warm-up scenario would not work because of the absence of heat sources. A recent chemical model attributed the presence of methanol and large organics to the efficient chemical desorption and a class of neutral-neutral reactions that proceed fast at low temperatures in the gas phase.
Aims: The model calls for a high abundance of methanol ice at the edge of the CO freeze-out zone in cold cloud cores.
Methods: We performed medium-resolution spectroscopy toward three field stars behind the starless core L 1544 at 3 μm to constrain the methanol ice abundance and compare it with the model predictions.
Results: One of the field stars shows a methanol ice abundance of 11% with respect to water ice. This is higher than the typical methanol abundance previously found in cold cloud cores (4%), but is 4.5 times lower than predicted. The reason for the disagreement between the observations and the model calculations is not yet understood.

Based on data collected by SpeX at the Infrared Telescope Facility (IRTF), which is operated by the University of Hawaii under contract NNH14CK55B with the National Aeronautics and Space Administration.