演講資訊

摘要：

Prestellar cores represent the initial conditions of star formation. At this stage, heavy molecules such as CO are significantly depleted in these cold, dense environments, limiting our ability to probe core centers. In contrast, deuterated molecular ions, particularly o-H2D+, emerge as key tracers due to enhanced deuterium fractionation at low temperatures. We present the first direct observation of o-H2D+ depletion in the prestellar core 205.46−14.56M3 using ALMA 820um continuum and o-H2D+(110-111) data at ~300au resolution. We confirm the previously reported two distinct substructures, B1 and B2, and identify a significant o-H2D+ depletion zone of ~600au in diameter toward B1 with a peak N2D+/N2H+ abundance ratio of ~1. Chemo-dynamical modeling reproduces the observed deuteration profiles with a core age of ~0.42Myr, comparable to the free-fall time. This suggests that the substructures formed via turbulent fragmentation through rapid contraction rather than through slow, quasi-static contraction. Our observations also reveal that the gas between B1 and B2 exhibits nearly thermal velocity dispersion, which is consistent with a turbulent scenario in which turbulence dissipates in no more than a few free-fall times. Our results highlight the critical role of deuterated ions in probing both the chemical evolution and dynamical state of dense cores.