We present a multiplicity study of all known protostars (94) in the Perseus molecular cloud from a Karl G. Jansky Very Large Array (VLA) survey at Ka-band (8 mm and 1 cm) and C-band (4 cm and 6.6 cm). The observed sample has a bolometric luminosity range between 0.1 L and ∼33 L , with a median of 0.7 L . This multiplicity study is based on the Ka-band data, having a best resolution of ∼0. 065 (15 AU) and separations out to ∼43 (10000 AU) can be probed. The overall multiplicity fraction (MF) is found to be of 0.40±0.06 and the companion star fraction (CSF) is 0.71±0.06. The MF and CSF of the Class 0 protostars are 0.57±0.09 and 1.2±0.2, and the MF and CSF of Class I protostars are both 0.23±0.08. The distribution of companion separations appears bimodal, with a peak at ∼75 AU and another peak at ∼3000 AU. Turbulent fragmentation is likely the dominant mechanism on >1000 AU scales and disk fragmentation is likely to be the dominant mechanism on <200 AU scales. Toward three Class 0 sources we find companions separated by <30 AU. These systems have the smallest separations of currently known Class 0 protostellar binary systems. Moreover, these close systems are embedded within larger (50 AU to 400 AU) structures and may be candidates for ongoing disk fragmentation.

We have conducted a survey of 328 protostars in the Orion molecular clouds with the Atacama Large Millimeter/ submillimeter Array at 0.87 mm at a resolution of ∼0 1 (40 au), including observations with the Very Large Array at 9mm toward 148 protostars at a resolution of ∼0 08 (32 au). This is the largest multiwavelength survey of protostars at this resolution by an order of magnitude. We use the dust continuum emission at 0.87 and 9mm to measure the dust disk radii and masses toward the Class 0, Class I, and flat-spectrum protostars, characterizing the evolution of these disk properties in the protostellar phase. The mean dust disk radii for the Class 0, Class I, and flat-spectrum protostars are -+ 44.9 3.4 5.8 , -+ 37.0 3.0 4.9 , and -+ 28.5 2.3 3.7 au, respectively, and the mean protostellar dust disk masses are 25.9 -+ 4.0 7.7 , -+ 14.9 2.2 3.8 , -+11.6 1.93.5 Å M , respectively. The decrease in dust disk masses is expected from disk evolution and accretion, but the decrease in disk radii may point to the initial conditions of star formation not leading to the systematic growth of disk radii or that radial drift is keeping the dust disk sizes small. At least 146 protostellar disks (35% of 379 detected 0.87 mm continuum sources plus 42 nondetections) have disk radii greater than 50 au in our sample. These properties are not found to vary significantly between different regions within Orion. The protostellar dust disk mass distributions are systematically larger than those of Class II disks by a factor of >4, providing evidence that the cores of giant planets may need to at least begin their formation during the protostellar phase.

Binary and multiple star systems are a frequent outcome of the star formation process 1;2 , and as a result, almost half of all sun-like stars have at least one companion star 3 . Theoretical studies indicate that there are two main pathways that can operate concurrently to form binary/multiple star systems: large scale fragmentation of turbulent gas cores and filaments 4;5 or smaller scale fragmentation of a massive protostellar disk due to gravitational instability 6;7 . Observational evidence for turbulent fragmentation on scales of >1000 AU has recently emerged 8;9 . Previous evidence for disk fragmentation was limited to inferences based on the separations of more-evolved pre-main sequence and protostellar multiple systems 10;11;12;13 . The triple protostar system L1448 IRS3B is an ideal candidate to search for evidence of disk fragmentation. L1448 IRS3B is in an early phase of the star formation process, likely less than 150,000 years in age 14 , and all protostars in the system are separated by <200 AU. Here we report observations of dust and molecular gas emission that reveal a disk with spiral structure surrounding the three protostars. Two protostars near the center of the disk are separated by 61 AU, and a tertiary protostar is coincident with a spiral arm in the outer disk at a 183 AU separation 13 . The inferred mass of the central pair of protostellar objects is ⇠1 M , while the disk surrounding the three protostars has a total mass of ⇠0.30 M . The tertiary protostar itself has a minimum mass of ⇠0.085 M . We demonstrate that the disk around L1448 IRS3B appears susceptible to disk fragmentation at radii between 150 AU and 320 AU, overlapping with the location of the tertiary protostar. This is consistent with models for a protostellar disk that has recently undergone gravitational instability, spawning one or two companion stars.L1448 IRS3B is located in the Perseus molecular cloud at a distance of ⇠230 pc 15 and contains three protostars out of the six that collectively make up L1448 IRS3 13;14 , spanning 0.05 pc. L1448 IRS3B is a Class 0 protostar system 16 , which signifies an early phase of the star formation process when the protostars are deeply enshrouded in an envelope of accreting material 17 . The three protostars in L1448 IRS3B (denoted -a, -b, and -c) have a hierarchical configuration; the central-most protostar, IRS3B-a, has projected separations from IRS3B-b and IRS3B-c of 61 AU and 183 AU, respectively 13 . The new observations of L1448 IRS3B conducted with the Atacama Large Millimeter/submillimeter Array (ALMA) at a resolution of 0. 00 27⇥0. 00 16 (62 AU ⇥ 37 AU) provide images at 1.3 mm of the dust and gas emission surrounding the three protostars with 10⇥ higher sensitivity and 2⇥ higher resolution than previous studies.The ALMA 1.3 mm image of L1448 IRS3B is shown in Figure 1, revealing dust emission toward each of the three distinct protostars identified in previous Karl G. Jansky Very Large Array (VLA) observations 13 . The ALMA images also reveal a disk with substructure sur...

Context. Recent years have seen building evidence that planet formation starts early, in the first ~0.5 Myr. Studying the dust masses available in young disks enables us to understand the origin of planetary systems given that mature disks are lacking the solid material necessary to reproduce the observed exoplanetary systems, especially the massive ones. Aims. We aim to determine if disks in the embedded stage of star formation contain enough dust to explain the solid content of the most massive exoplanets. Methods. We use Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 (1.1–1.3 mm) continuum observations of embedded disks in the Perseus star-forming region together with Very Large Array (VLA) Ka-band (9 mm) data to provide a robust estimate of dust disk masses from the flux densities measured in the image plane. Results. We find a strong linear correlation between the ALMA and VLA fluxes, demonstrating that emission at both wavelengths is dominated by dust emission. For a subsample of optically thin sources, we find a median spectral index of 2.5 from which we derive the dust opacity index β = 0.5, suggesting significant dust growth. Comparison with ALMA surveys of Orion shows that the Class I dust disk mass distribution between the two regions is similar, but that the Class 0 disks are more massive in Perseus than those in Orion. Using the DIANA opacity model including large grains, with a dust opacity value of κ9 mm = 0.28 cm2 g−1, the median dust masses of the embedded disks in Perseus are 158 M⊕ for Class 0 and 52 M⊕ for Class I from the VLA fluxes. The lower limits on the median masses from ALMA fluxes are 47 M⊕ and 12 M⊕ for Class 0 and Class I, respectively, obtained using the maximum dust opacity value κ1.3 mm = 2.3 cm2 g−1. The dust masses of young Class 0 and I disks are larger by at least a factor of ten and three, respectively, compared with dust masses inferred for Class II disks in Lupus and other regions. Conclusions. The dust masses of Class 0 and I disks in Perseus derived from the VLA data are high enough to produce the observed exoplanet systems with efficiencies acceptable by planet formation models: the solid content in observed giant exoplanets can be explained if planet formation starts in Class 0 phase with an efficiency of ~15%. A higher efficiency of ~30% is necessary if the planet formation is set to start in Class I disks.

The mechanism for producing polarized emission from protostellar disks at (sub)millimeter wavelengths is currently uncertain. Classically, polarization is expected from non-spherical grains aligned with the magnetic field. Recently, two alternatives have been suggested. One polarization mechanism is caused by self-scattering from dust grains of sizes comparable with the wavelength, while the other mechanism is due to grains aligned with their short axes along the direction of radiation anisotropy. The latter has recently been shown as a likely mechanism for causing the dust polarization detected in HL Tau at 3.1 mm. In this paper, we present ALMA polarization observations of HL Tau for two more wavelengths: 870 μm and 1.3 mm. The morphology at 870 μm matches the expectation for self-scattering, while that at 1.3 mm shows a mix between self-scattering and grains aligned with the radiation anisotropy. The observations cast doubt on the ability of (sub)millimeter continuum polarization to probe disk magnetic fields for at least HL Tau. By showing two distinct polarization morphologies at 870 μm and 3.1 mm and a transition between the two at 1.3 mm, this paper provides definitive evidence that the dominant (sub)millimeter polarization mechanism transitions with wavelength. In addition, if the polarization at 870 μm is due to scattering, the lack of polarization asymmetry along the minor axis of the inclined disk implies that the large grains responsible for the scattering have already settled into a geometrically thin layer, and the presence of asymmetry along the major axis indicates that the HL Tau disk is not completely axisymmetric.

Emission from protostars at centimeter radio wavelengths has been shown to trace the free–free emission arising from ionizing shocks as a result of jets and outflows driven by protostars. Therefore, measuring properties of protostars at radio frequencies can provide valuable insights into the nature of their outflows and jets. We present a C-band (4.1 and 6.4 cm) survey of all known protostars (Class 0 and Class I) in Perseus as part of the VLA Nascent Disk and Multiplicity (VANDAM) Survey. We examine the known correlations between radio flux density and protostellar parameters, such as bolometric luminosity and outflow force, for our sample. We also investigate the relationship between radio flux density and far-infrared line luminosities from Herschel. We show that free–free emission most likely originates from J-type shocks; however, the large scatter indicates that those two types of emission probe different time and spatial scales. Using C-band fluxes, we removed an estimation of free–free contamination from the corresponding Ka-band (9 mm) flux densities that primarily probe dust emission from embedded disks. We find that the compact (<1″) dust emission is lower for Class I sources (median dust mass 96 M ⊕) relative to Class 0 (248 M ⊕), but several times higher than in Class II (5–15 M ⊕). If this compact dust emission is tracing primarily the embedded disk, as is likely for many sources, this result provides evidence of decreasing disk masses with protostellar evolution, with sufficient mass for forming giant planet cores primarily at early times.

Binary formation is an important aspect of star formation. One possible route for close-in binary formation is disk fragmentation [1,2,3] . Recent observations show small scale asymmetries (<300 au) around young protostars [2,4] , although not always resolving the circumbinary disk, are linked to disk phenomena [5,6] . In later stages, resolved circumbinary disk observations [7] (<200 au) show similar asymmetries, suggesting the origin of the asymmetries arises from binary-disk interactions [8,9,10] . We observed one of the youngest systems to study the connection between disk and dense core. We find for the first time a bright and clear streamer in chemically fresh material (Carbon-chain species) that originates from outside the dense core (>10,500 au). This material connects the outer dense core with the region where asymmetries arise near disk scales. This new structure type, 10x larger than those seen near disk scales, suggests a different interpretation of previous observations: largescale accretion flows funnel material down to disk scales. These results reveal the underappreciated importance of the local environment on the formation and evolution of disks in early systems [13,14] and a possible initial condition for the formation of annular features in young disks [15,16] .

Annular structures, or rings and gaps, in disks around pre-main sequence stars have been detected in abundance towards Class II objects ~1,000,000 years in age 1 . These structures are often interpreted as evidence of planet formation 1,2,3 , with planet-mass bodies carving rings and gaps in the disk 4 . This implies that planet formation may already be underway in even younger disks in the Class I phase, when the protostar is still embedded in a larger scale dense envelope of gas and dust 5 . While younger disks likely play an important role in the onset of planet formation, only within the past decade have detailed properties of disks in the youngest star-forming phases begun to be observed 6,7 . Here we present 1.3 mm dust emission observations with 5 au resolution that show four annular substructures in the disk of the young (<500,000 years [8] ) protostar IRS 63. IRS 63, a single Class I source located in the nearby Ophiuchus molecular cloud (at a distance of 144 pc [9] ), is one of the brightest Class I protostars at (sub)millimeter wavelengths that also has a relatively large disk (>50 au) [10] . Multiple annular substructures observed towards disks at young times can act as an early foothold for dust grain growth, a prerequisite of planet formation. Whether planets already exist or not in the disk of IRS 63, it is clear that the planet formation process begins in the young protostellar phases, earlier than predicted by current planet formation theories 11 .We studied the disk of IRS 63 with 5 au resolution via observing the emission from dust grains with the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.3 mm. These observations revealed two concentric bright annular substructures (ring-like, R1 and R2) and two dark annular substructures (gaplike, G1 and G2), shown in Fig. 1. While dust structures within disks of Class I protostars have been previously observed 2,12-14 , IRS 63 is the least evolved protostellar disk with multiple concentric dust annular substructures as indicated by different evolutionary indicators (see Methods). The annular substructures we observe towards the disk of the young protostar IRS 63 indicate that conditions for of 1 26