Deuterium fractionation of the starless core L 1498

Context . Molecular deuteration is commonly seen in starless cores and is expected to occur on a timescale comparable to that of the core contraction. Thus, the deuteration serves as a chemical clock, allowing us to investigate dynamical theories of core formation. Aims . We aim to provide a 3D cloud description for the starless core L 1498 located in the nearby low-mass star-forming region Taurus and explore its possible core formation mechanism. Methods . We carried out nonlocal thermal equilibrium radiative transfer with multi-transition observations of the high-density tracer N 2 H + to derive the density and temperature profiles of the L 1498 core. By combining these observations with the spectral observations of the deuterated species, ortho-H 2 D + , N 2 D + , and DCO + , we derived the abundance profiles for the observed species and performed chemical modeling of the deuteration profiles across L 1498 to constrain the contraction timescale. Results . We present the first ortho-H 2 D + (1 10 −1 11 ) detection toward L 1498. We find a peak molecular hydrogen density of 1.6 −0.3 +3.0 × 10 5 cm −3 , a temperature of 7.5 −0.5 +0.7 K, and a N 2 H + deuteration of 0.27 −0.15 +0.12 in the center. Conclusions . We derived a lower limit of the core age for L 1498 of 0.16 Ma, which is compatible with the typical free-fall time, indicating that L 1498 likely formed rapidly.