Early Planet Formation in Embedded Disks (eDisk). IX. High-resolution ALMA Observations of the Class 0 Protostar R CrA IRS5N and Its Surroundings

Abstract

We present high-resolution high-sensitivity observations of the Class 0 protostar RCrA IRS5N as part of the Atacama Large Milimeter/submilimeter Array large program Early Planet Formation in Embedded Disks. The 1.3 mm continuum emission reveals a flattened continuum structure around IRS5N, consistent with a protostellar disk in the early phases of evolution. The continuum emission appears smooth and shows no substructures. However, a brightness asymmetry is observed along the minor axis of the disk, suggesting that the disk is optically and geometrically thick. We estimate the disk mass to be between 0.007 and 0.02 M _⊙ . Furthermore, molecular emission has been detected from various species, including C ^18 O (2–1), ^12 CO (2–1), ^13 CO (2–1), and H _2 CO (3 _0,3 − 2 _0,2 , 3 _2,1 − 2 _2,0 , and 3 _2,2 − 2 _2,1 ). By conducting a position–velocity analysis of the C ^18 O (2–1) emission, we find that the disk of IRS5N exhibits characteristics consistent with Keplerian rotation around a central protostar with a mass of approximately 0.3 M _⊙ . Additionally, we observe dust continuum emission from the nearby binary source IRS5a/b. The emission in ^12 CO toward IRS5a/b seems to emanate from IRS5b and flow into IRS5a, suggesting material transport between their mutual orbits. The lack of a detected outflow and large-scale negatives in ^12 CO observed toward IRS5N suggests that much of the flux from IRS5N is being resolved out. Using a 1D radiative transfer model, we infer the mass of the envelope surrounding IRS5N to be ∼1.2 M _⊙ . Due to this substantial surrounding envelope, the central IRS5N protostar is expected to be significantly more massive in the future.

Keywords

• Protostars
• Young stellar objects
• Protoplanetary disks
• Interstellar medium