Early Planet Formation in Embedded Disks (eDisk). II. Limited Dust Settling and Prominent Snow Surfaces in the Edge-on Class I Disk IRAS 04302+2247

Abstract

While dust disks around optically visible, Class II protostars are found to be vertically thin, when and how dust settles to the midplane are unclear. As part of the Atacama Large Millimeter/submillimeter Array large program, Early Planet Formation in Embedded Disks, we analyze the edge-on, embedded, Class I protostar IRAS 04302+2247, also nicknamed the “Butterfly Star.” With a resolution of 0.″05 (8 au), the 1.3 mm continuum shows an asymmetry along the minor axis that is evidence of an optically thick and geometrically thick disk viewed nearly edge-on. There is no evidence of rings and gaps, which could be due to the lack of radial substructure or the highly inclined and optically thick view. With 0.″1 (16 au) resolution, we resolve the 2D snow surfaces, i.e., the boundary region between freeze-out and sublimation, for 12CO J = 2–1, 13CO J = 2–1, C18O J = 2–1, H 2CO J = 30,3–20,2, and SO J = 65–54, and constrain the CO midplane snow line to ∼130 au. We find Keplerian rotation around a protostar of 1.6 ± 0.4 M ⊙ using C18O. Through forward ray-tracing using RADMC-3D, we find that the dust scale height is ∼6 au at a radius of 100 au from the central star and is comparable to the gas pressure scale height. The results suggest that the dust of this Class I source has yet to vertically settle significantly.

Early Planet Formation in Embedded Disks (eDisk). IV. The Ringed and Warped Structure of the Disk around the Class I Protostar L1489 IRS

“…The direction of the shift indicates that the southern side is the far side of the disk, which is consistent with the outflow configuration, in which the southern lobe is blueshifted (Yen et al 2014). Similar molecular line structures elevated from the midplane have been observed in a number of disks (e.g., Law et al 2021bLaw et al , 2022Lin et al 2023). Furthermore, the 13 CO and C 18 O emissions show higher brightness temperatures on the southwestern side of the inner (r  0 5) disk (Figure 3).…”

“…As the disk column density decreases with radius, photodesorption due to penetrating UV radiation could keep CO in the gas phase outside a certain radius. A similar re-enhancement of the line emission at an outer radius is also observed in several disks (Dutrey et al 2017;Flores et al 2021;Lin et al 2023). In Class II disks, similar secondary CO snowlines have also been suggested by the double emission rings of DCO + , which is expected to trace the gas-phase CO (Öberg et al 2015;Cataldi et al 2021).…”

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

“…These structures can be explained by a geometric effect, which is a combination of the optical depth effect and disk flaring. When the dust continuum emission of an inclined disk is optically thick, we look at a cold disk edge on one side of the plane of the sky but look at a warm disk surface on the other side along the minor axis (e.g., Villenave et al 2020, Lin et al 2023. If this is the case for Ced110 IRS4A, the southern side (brighter side) corresponds to the disk surface facing the observer.…”

Early Planet Formation in Embedded Disks (eDisk). III. A First High-resolution View of Submillimeter Continuum and Molecular Line Emission toward the Class 0 Protostar L1527 IRS

“…An asymmetry along the minor axis of a near-edge-on disk can be explained by a vertically extended optically thick dust disk. In this scenario, warmer material is observed toward the back side of the disk because the emission would get optically thick already in the colder outer disk on the near side (e.g., Ohashi et al 2022 and Figure 3 therein;Lin et al 2023;S. Takakuwa et al 2023, in preparation).…”