CB17: Inferring the dynamical history of a prestellar core with chemo-dynamical models

Abstract

We present a detailed theoretical study of the isolated Bok globule CB17 (L1389) based on spectral maps of CS, HCO${}^{+}$, C${}^{18}$O, C${}^{34}$S, and H${}^{13}$CO${}^{+}$ lines. A phenomenological model of prestellar core evolution, a time-dependent chemical model, and a radiative transfer simulation for molecular lines are combined to reconstruct the chemical and kinematical structure of this core. We developed a general criterion that allows to quantify the difference between observed and simulated spectral maps. By minimizing this difference, we find that very high and very low values of the effective sticking probability $S$ are not appropriate for the studied prestellar core. The most probable $S$ value for CB17 is 0.3--0.5. The spatial distribution of the intensities and self-absorption features of optically thick lines is indicative of UV irradiation of the core. By fitting simultaneously optically thin and optically thick transitions, we isolate the model that reproduces all the available spectral maps to a reasonable accuracy. The line asymmetry pattern in CB17 is reproduced by a combination of infall, rotation, and turbulent motions with velocities $\sim 0.05$ km s${}^{-1}$, $\sim 0.1$ km s${}^{-1}$, and $\sim 0.1$ km s${}^{-1}$, respectively. These parameters corresponds to energy ratios $E_{\mathrm{rot}}/E_{\mathrm{grav}}\approx 0.03$, $E_{\mathrm{therm}}/E_{\mathrm{grav}}\approx 0.8$, and $E_{\mathrm{turb}}/E_{\mathrm{grav}}\approx 0.05$ (the rotation parameters are determined for $i=90^{\circ }$). The chemical age of the core is about 2 Myrs. In particular, this is indicated by the central depletion of CO, CS, and HCO${}^{+}$. Based on the angular momentum value, we argue that the core is going to fragment, i.e., to form a binary (multiple) star. (abridged)

arXiv commentApJ, in press

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