Witnessing the birth of a binary

ABSTRACT :
Recently, the ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP) targeted 72 starless or protostellar cores in the Orion A, B, and λ Orionis clouds, sampled from the previous JCMT SCOPE program. Among these three clouds, Orion B exhibits the highest companion star fraction, resulting in a variety of protostellar binary/multiple systems ranging from single stars to five-star systems. One of the key questions is the origin of the stellar multiplicity. Fragmented substructures in the starless cores are expected to form multiple stellar systems. However, such substructures are rarely observed during the starless phase. G205.46M3, a low-mass starless core in Orion B with a mass of 2.2 Msol, provides a great laboratory for studying core fragmentation as it represents a unique starless core harboring two substructures in the kilo-au scale, as identified by ALMASOP. Molecules are excellent tracers of physical conditions, with deuterated species offering further insight into evolutionary processes. In this presentation, we will present our new ALMA data with ortho-H2D+, N2D+, and N2H+. These molecules serve as a chemical clock to assess if the collapse of G205.46M3 follows the free-fall timescale suggested by turbulent-dominant core fragmentation. Notably, we also report the first discovery of ortho-H2D+ depletion.