2023ApJ...954..101A

Precise estimates of protostellar masses are crucial to characterize the formation of stars of low masses down to brown dwarfs (BDs; M_* < 0.08 M_☉). The most accurate estimation of protostellar mass uses the Keplerian rotation in the circumstellar disk around the protostar. To apply the Keplerian rotation method to a protostar at the low-mass end, we have observed the Class 0 protostar IRAS 16253-2429 using the Atacama Large Millimeter/submillimeter Array (ALMA) in the 1.3 mm continuum at an angular resolution of 0.″07 (10 au), and in the ¹²CO, C¹⁸O, ¹³CO (J = 2-1), and SO (J_N = 6₅-5₄) molecular lines, as part of the ALMA Large Program Early Planet Formation in Embedded Disks project. The continuum emission traces a nonaxisymmetric, disk-like structure perpendicular to the associated ¹²CO outflow. The position-velocity (PV) diagrams in the C¹⁸O and ¹³CO lines can be interpreted as infalling and rotating motions. In contrast, the PV diagram along the major axis of the disk-like structure in the ¹²CO line allows us to identify Keplerian rotation. The central stellar mass and the disk radius are estimated to be ∼0.12-0.17 M_☉ and ∼13-19 au, respectively. The SO line suggests the existence of an accretion shock at a ring (r ∼ 28 au) surrounding the disk and a streamer from the eastern side of the envelope. IRAS 16253-2429 is not a proto-BD but has a central stellar mass close to the BD mass regime, and our results provide a typical picture of such very-low-mass protostars.