2017A&A...606A.142C

In dense and cold molecular clouds dust grains are surrounded by thick icy mantles. It is not clear, however, if dust growth and coagulation take place before the protostar switches on. This is an important issue as the presence of large grains may affect the chemical structure of dense cloud cores, including the dynamically important ionization fraction and the future evolution of solids in protoplanetary disks. To study this further, we focus on L1544 - one of the most centrally concentrated pre-stellar cores on the verge of star formation - which has a well-known physical structure. We observed L1544 at 1.2 and 2mm using NIKA, a new receiver at the IRAM 30m telescope, and we used data from the Herschel Space Observatory archive. We find no evidence of grain growth toward the center of L1544 at the available angular resolution. Therefore, we conclude that single-dish observations do not allow us to investigate grain growth toward the pre-stellar core L1544 and high-sensitivity interferometer observations are needed. We predict that dust grains can grow to 200µm in size toward the central ∼300au of L1544. This implies a dust opacity change of a factor of ∼2.5 at 1.2mm, which can be detected using the Atacama Large Millimeter and submillimeter Array (ALMA) at different wavelengths and with an angular resolution of 2''.