Water and Methanol Ice in L 1544

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. © ESO 2021. Acknlwo edgemen. M.G. thanks all the staff and crew of the IRTF, in particular, Mike Connelley, Brian Cabreira, Dave Griep, Miranda Hawarden-Ogata and Bobby Bus who kindly helped conducting the observation from Munich. We would like to thank the hospitality of the Hawaiian community that made the research presented here possible. My sincere appreciation goes to Jorma Harju and Viktor Zivkov who gave me thorough instructions how to construct dust emission / color temperature maps, and a color extinction map, respectively. We thank Wing-Fai Thi for the fruitful discussion about the influence of dust grain size on the shape of methanol ice absorption feature. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. The optical spectra of the ice was taken from Sackler Laboratory Ice Database. This research has made use of NASA’s Astrophysics Data System. This research has made use of the SIM-BAD database, operated at CDS, Strasbourg, France. M.G. is supported by the German Research Foundation (DFG) grant GO 1927/6-1. The work of A.I.V. is supported by the Russian Ministry of Science and Higher Education via the State Assignment project FEUZ-2020-0038. A.I.V. is a head of the Max Planck Partner Group at the Ural Federal University. I.J.-S. has received partial support from the Spanish FEDER (ESP2017-86582-C4-1-R) and the State Research Agency (AEI; PID2019-105552RB-C41). C.R.-Z. acknowledges support from program UNAM-DGAPA IN112620, Mexico. The authors thank the anonymous referee for the valuable suggestions that have significantly improved the manuscript.