2018ApJ...856..147O

We have investigated the TUKH122 prestellar core in the Orion A cloud using ALMA 3 mm dust continuum, N₂H⁺ (J = 1-0), and CH₃OH (J_K=2_K-1_K) molecular-line observations. Previous studies showed that TUKH122 is likely on the verge of star formation because the turbulence is almost dissipated and chemically evolved among other starless cores in the Orion A cloud. By combining ALMA 12 m and ACA data, we recover extended emission with a resolution of ∼5'' corresponding to 0.01 pc and identify six condensations with a mass range of 0.1-0.4 M_☉ and a radius of <=0.01 pc. These condensations are gravitationally bound following a virial analysis and are embedded in the filament, including the elongated core with a mass of ∼29 M_☉ and a radial density profile of r^–1.6 derived by Herschel. The separation of these condensations is ∼0.035 pc, consistent with the thermal Jeans length at a density of 4.4 x 10⁵ cm^–3. This density is similar to the central part of the core. We also find a tendency for the N₂H⁺ molecule to deplete at the dust peak condensation. This condensation may be beginning to collapse because the line width becomes broader. Therefore, the fragmentation still occurs in the prestellar core by thermal Jeans instability, and multiple stars are formed within the TUKH122 prestellar core. The CH₃OH emission shows a large shell-like distribution and surrounds these condensations, suggesting that the CH₃OH molecule formed on dust grains is released into the gas phase by nonthermal desorption such as photoevaporation caused by cosmic-ray-induced UV radiation.