Oral Presentation

Early Planet Formation in Embedded Disks (eDisk): An Extremely Small Keplerian Disk in the Class 0 Protostar IRAS 15398-3359

Author(s): Travis Thieme (NTHU), Shih-Ping Lai (NTHU)

Presenter: Shih-Ping Lai (National Tsing Hua University)

Protostellar disks are a ubiquitous part of the star formation process and the future sites of planet formation. In this paper, we present the first-look at the high angular resolution dust continuum ($\sim40\,$mas or $6\,$au) and molecular line (~150 mas or 23 au) results from the Early Planet Formation in Embedded Disks (eDisk) large program of the young, Class 0 protostar, IRAS 15398-3359. The dust continuum traces a large-scale structure within the bipolar outflows as also seen in previous observations of this source, while the higher angular resolution image reveals a compact continuum structure with a deconvolved size of 29 mas x 18 mas (4.5 au x 2.8 au), a position angle of 117 deg and an inclination angle of ~51 deg from 2D Gaussian fitting and geometric estimations. We estimate the disk mass from the compact component to be 0.48 M_jup-1.31 M_jup, indicating the disk is very low-mass. The molecular lines of C$^{18}$O ($2-1$), $^{13}$CO ($2-1$), $^{12}$CO ($2-1$) and SO ($6_5-5_4$) are all detected and trace components of the protostellar disk, infalling-rotating envelope and bipolar outflows. We analyze and fit the position-velocity (PV) diagrams of the SO emission and find that overall, the emission is more consistent with a power-law profile of $v\sim r^{-1}$, indicative of infall with conserved angular momentum. When fitting the higher velocity portions of the PV diagram, we recover a rotation profile of $v\sim r^{-0.63}$, which is closer and tending more towards the Keplerian rotation profile of $v\sim r^{-0.5}$ when moving to higher velocities. From this, disk radius is estimated to be less than 20$\,$au with a protostellar mass likely between $0.02\,M_\odot - 0.05\,M_\odot$, meaning the protostar is very low-mass and the disk is very small. Offsets in the position angles of the continuum disk and outflow further perpetuate the idea that the IRAS 15398-3359 system is precessing. These results highlight the importance of high-resolution observations and various molecular tracers to understand the protostellar properties of young Class 0 systems.