  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 WL 17. We used ALMA 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 12CO and C18O (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 base of both blue-shifted and red-shifted outflows based on
the 12CO emission, which is clearly associated with the disk around WL 17. The
outflow mass ejection rate is ~3.6x10^-7 Msun yr-1 and the dynamical timescale
is as short as ~ 10^4 yr. The C18O 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 planet formation and dust growth scenarios in the
accretion phase of star formation.
