Deuterium fractionation of the starless core L 1498

Abstract

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. 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 the possible core formation mechanism of L 1498. We carried out non-local 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. Combining with the spectral observations of the deuterated species, ortho-H${}_2$D${}^{+}$, N${}_2$D${}^{+}$, and DCO${}^{+}$, we derived the abundance profiles for observed species and performed chemical modeling of the deuteration profiles across L 1498 to constrain the contraction timescale. We present the first ortho-H${}_2$D${}^{+}$ (1${}_{10}$-1${}_{11}$) detection toward L 1498. We find a peak molecular hydrogen density of $1.6_{-0.3}^{+3.0}\times 10^5$~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. We derive 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.

21 pages, 12 figures, accepted for publication in A&A

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