We report Atacama Large Millimeter/submillimeter Array (ALMA) cycle 0 observations of C 18 O (J = 2 − 1), SO (J N = 6 5 − 5 4 ) and 1.3 mm dust continuum toward L1527 IRS, a class 0 solar-type protostar surrounded by an infalling and rotating envelope. C 18 O emission shows strong redshifted absorption against the bright continuum emission associated with L1527 IRS, strongly suggesting infall motions in the C 18 O envelope. The C 18 O envelope also rotates with a velocity mostly proportional to r −1 , where r is the radius, while the rotation profile at the -2innermost radius (∼54 AU) may be shallower than r −1 , suggestive of formation of a Keplerian disk around the central protostar of ∼ 0.3 M ⊙ in dynamical mass. SO emission arising from the inner part of the C 18 O envelope also shows rotation in the same direction as the C 18 O envelope. The rotation is, however, rigid-body like which is very different from the differential rotation shown by C 18 O. In order to explain the line profiles and the position-velocity (PV) diagrams of C 18 O and SO observed, simple models composed of an infalling envelope surrounding a Keplerian disk of 54 AU in radius orbiting a star of 0.3 M ⊙ are examined. It is found that in order to reproduce characteristic features of the observed line profiles and PV diagrams, the infall velocity in the model has to be smaller than the free-fall velocity yielded by a star of 0.3 M ⊙ . Possible reasons for the reduced infall velocities are discussed.

We present ALMA 1.3 mm continuum, 12 CO, C 18 O, and SO data for the Class 0 protostars, Lupus 3 MMS, IRAS 15398−3559, and IRAS 16253−2429 at resolutions of ∼100 AU. By measuring a rotational profile in C 18 O, a 100 AU Keplerian disk around a 0.3 M ⊙ protostar is observed in Lupus 3 MMS. No 100 AU Keplerian disks are observed in IRAS 15398−3559 and IRAS 16253−2429. Nevertheless, embedded compact (<30 AU) continuum components are detected. The C 18 O emission in IRAS 15398−3559 shows signatures of infall with a constant angular momentum. IRAS 16253−2429 exhibits signatures of infall and rotation, but its rotational profile is unresolved. By fitting the C 18 O data with our kinematic models, the protostellar masses and the disk radii are inferred to be 0.01 M ⊙ and 20 AU in IRAS 15398−3559, and 0.03 M ⊙ and 6 AU in IRAS 16253−2429. By comparing the specific angular momentum profiles from 10,000 to 100 AU in 8 Class 0 and I protostars, we find that the evolution of envelope rotation can be described with conventional inside-out collapse models. In comparison with a sample of 18 protostars with known disk radii, our results reveal signs of disk growth, with the disk radius increasing as M * 0.8±0.14 or t 1.09±0.37 in the Class 0 stage, where M * is the protostellar mass and t is the age. The disk growth rate slows down in the Class I stage. Besides, we find a hint that the mass accretion rate declines as t −0.26±0.04 from the Class 0 to I stages.

We have observed the Class I protostar TMC-1A with Atacama Millimeter/submillimeter Array (ALMA) in the emissions of 12 CO and C 18 O (J = 2−1), and

We have conducted ALMA observations in the 1.3 mm continuum and 12 CO (2-1), C 18 O (2-1) and SO (5 6 -4 5 ) lines toward L1489 IRS, a Class I protostar surrounded by a Keplerian disk and an infalling envelope. The Keplerian disk is clearly identified in the 12 CO and C 18 O emission, and its outer radius (∼700 AU) and mass (∼0.005 M ⊙ ) are comparable to those of disks around T Tauri stars. The protostellar mass is estimated to be 1.6 M ⊙ with the inclination angle of 66 • . In addition to the Keplerian disk, there are blueshifted and redshifted off-axis protrusions seen in the C 18 O emission pointing toward the north and the south, respectively, adjunct to the middle part of the Keplerian disk. The shape and kinematics of these protrusions can be interpreted as streams of infalling flows with a conserved angular momentum following parabolic trajectories toward the Keplerian disk, and the mass infalling rate is estimated to be ∼5 × 10 −7 M ⊙ yr −1 . The specific angular momentum of the infalling flows (∼2.5 × 10 −3 km s −1 pc) is comparable to that at the outer radius of the Keplerian disk (∼4.8 × 10 −3 km s −1 pc). The SO emission is elongated along the disk major axis and exhibits a linear velocity gradient along the axis, which is interpreted as that the SO emission

We have newly observed the Class 0/I protostar L1527 IRS using the Atacama Large Millimeter/submillimeter Array (ALMA) during its Cycle 1 in 220 GHz dust continuum and C 18 O (J = 2 − 1) line emissions with a ∼ 2 times higher angular resolution (∼ 0. ′′ 5) and ∼ 4 times better sensitivity than our ALMA Cycle 0 observations. Continuum emission shows elongation perpendicular to the associated outflow, with a deconvolved size of 0. ′′ 53 × 0. ′′ 15. C 18 O emission shows similar elongation, indicating that both emissions trace the disk and the flattened envelope surrounding the protostar. The velocity gradient of the C 18 O emission along the elongation due to rotation of the disk/envelope system is re-analyzed, identifying Keplerian rotation proportional to r −0.5 more clearly than the Cycle 0 observations. The Keplerian-disk radius and the dynamical stellar mass are kinematically estimated to be ∼ 74 AU and ∼ 0.45 M ⊙ , respectively. The continuum visibility is fitted by models without any annulus averaging, revealing that the disk is in hydrostatic equilibrium. The best-fit model also suggests a density jump by a factor of ∼ 5 between the disk and the envelope, suggesting that disks around protostars can be geometrically distinguishable from the envelope from a viewpoint of density contrast. Importantly, the disk radius geometrically identified with the density jump is consistent with the radius kinematically estimated. Possible origin of the density jump due to the mass accretion from the envelope to the disk is discussed. C 18 O observations can be reproduced by the same geometrical structures derived from the dust observations, with possible C 18 O freeze-out and localized C 18 O desorption.