Early Planet Formation in Embedded Disks (eDisk). V. Possible Annular Substructure in a Circumstellar Disk in the Ced110 IRS4 System

We have observed the Class 0/I protostellar system Ced110 IRS4 at an angular resolution of 0.'' 05(similar to 10 au)as part of the Atacama Large Millimeter/submillimeter Array large program, Early Planet Formation in Embedded Disks. The 1.3 mm dust continuum emission reveals that Ced110 IRS4 is a binary system with a projected separation of similar to 250 au. The continuum emissions associated with the main source and its companion, named Ced110 IRS4A andIRS4B, respectively, exhibit disk-like shapes and likely arise from dust disks around the protostars. The continuum emission of Ced110 IRS4A has a radius of similar to 110 au (similar to 0.'' 6)and shows bumps along its major axis with anasymmetry. The bumps can be interpreted as a shallow, ring-like structure at a radius of similar to 40 au(similar to 0.'' 2)in the continuum emission, as demonstrated from two-dimensional intensity distribution models. A rotation curve analysis on the (CO)-O-18 and (CO)-C-13 J=2-1 lines reveals the presence of a Keplerian disk within a radius of 120 au around Ced110 IRS4A, which supports the interpretation that the dust continuum emission arises from a disk. The ring-like structure in the dust continuum emission might indicate a possible annular substructure in the surface density of the embedded disk, although the possibility that it is an apparent structure due to the optically thick continuum emission cannot be ruled out.