We report high-resolution ALMA observations toward a massive protostellar core C1-Sa (∼30 M⊙) in the Dragon Infrared Dark Cloud. At the resolution of 140 AU, the core fragments into two kernels (C1-Sa1 and C1-Sa2) with a projected separation of ∼1400 AU along the elongation of C1-Sa, consistent with a Jeans length scale of ∼1100 AU. Radiative transfer modeling using RADEX indicates that the protostellar kernel C1-Sa1 has a temperature of ∼75 K and a mass of 0.55 M⊙. C1-Sa1 also likely drives two bipolar outflows, one being parallel to the plane-of-the-sky. C1-Sa2 is not detected in line emission and does not show any outflow activity but exhibits ortho-H2D+ and N2D+ emission in its vicinity, thus it is likely still starless. Assuming a 20 K temperature, C1-Sa2 has a mass of 1.6 M⊙. At a higher resolution of 96 AU, C1-Sa1 begins to show an irregular shape at the periphery, but no clear sign of multiple objects or disks. We suspect that C1-Sa1 hosts a tight binary with inclined disks and outflows. Currently, one member of the binary is actively accreting while the accretion in the other is significantly reduced. C1-Sa2 shows hints of fragmentation into two sub-kernels with similar masses, which requires further confirmation with higher sensitivity.
@article{arxiv.2305.02286,
title = {Binary Formation in a 100 $\mu$m-dark Massive Core},
author = {Shuo Kong and Héctor G. Arce and John J. Tobin and Yichen Zhang and María José Maureira and Kaitlin M. Kratter and Thushara G. S. Pillai},
journal= {arXiv preprint arXiv:2305.02286},
year = {2023}
}