Ring Gap Structure around Class I Protostar WL 17

Abstract

WL 17 is a Class I object and was considered to have a ring–hole structure. We analyzed the structure around WL 17 to investigate the detailed properties of this object. We used Atacama Large Millimeter/submillimeter Array archival data, which have a higher angular resolution than previous observations. We investigated the WL 17 system with the 1.3 mm dust continuum and ^12 CO and C ^18 O ( J = 2–1) line emissions. The dust continuum emission showed a clear ring structure with inner and outer edges of ∼11 and ∼21 au, respectively. In addition, we detected an inner disk of <5 au radius enclosing the central star within the ring, the first observation of this structure. Thus, WL 17 has a ring–gap structure, not a ring–hole structure. We did not detect any marked emission in either the gap or inner disk, indicating that there is no sign of a planet, circumplanetary disk, or binary companion. We identified the source of both blueshifted and redshifted outflows based on the ^12 CO emission, which is clearly associated with the disk around WL 17. The outflow mass ejection rate is ∼3.6 × 10 ^−7 M _⊙ yr ^−1 and the dynamical timescale is as short as ∼10 ^4 yr. The C ^18 O emission showed that an inhomogeneous infalling envelope, which can induce episodic mass accretion, is distributed in the region within ∼1000 au from the central protostar. With these new findings, we can constrain the scenarios of planet formation and dust growth in the accretion phase of star formation.

Keywords

• Protoplanetary disks
• Circumstellar disks
• Star formation
• Young stellar objects