An official website of the United States government
Abstract Understanding how material accretes onto the rotationally supported disk from the surrounding envelope of gas and dust in the youngest protostellar systems is important for describing how disks are formed. Magnetohydrodynamic simulations of magnetized, turbulent disk formation usually show spiral-like streams of material (accretion flows) connecting the envelope to the disk. However, accretion flows in these early stages of protostellar formation still remain poorly characterized, due to their low intensity, and possibly some extended structures are disregarded as being part of the outflow cavity. We use ALMA archival data of a young Class 0 protostar, Lupus 3-MMS, to uncover four extended accretion flow–like structures in C 18 O that follow the edges of the outflows. We make various types of position–velocity cuts to compare with the outflows and find the extended structures are not consistent with the outflow emission, but rather more consistent with a simple infall model. We then use a dendrogram algorithm to isolate five substructures in position–position–velocity space. Four out of the five substructures fit well (>95%) with our simple infall model, with specific angular momenta between 2.7–6.9 × 10 −4 km s −1 pc and mass-infall rates of 0.5–1.1 × 10 −6 M ⊙ yr −1 . Better characterization of the physical structure in the supposed “outflow cavities” is important to disentangle the true outflow cavities and accretion flows.
more »
« less
Disk Wind Feedback from High-mass Protostars. II. The Evolutionary Sequence
Abstract Star formation is ubiquitously associated with the ejection of accretion-powered outflows that carve bipolar cavities through the infalling envelope. This feedback is expected to be important for regulating the efficiency of star formation from a natal prestellar core. These low-extinction outflow cavities greatly affect the appearance of a protostar by allowing the escape of shorter-wavelength photons. Doppler-shifted CO line emission from outflows is also often the most prominent manifestation of deeply embedded early-stage star formation. Here, we present 3D magnetohydrodynamic simulations of a disk wind outflow from a protostar forming from an initially 60M⊙core embedded in a high-pressure environment typical of massive star-forming regions. We simulate the growth of the protostar fromm*= 1M⊙to 26M⊙over a period of ∼100,000 yr. The outflow quickly excavates a cavity with a half opening angle of ∼10° through the core. This angle remains relatively constant until the star reaches 4M⊙. It then grows steadily in time, reaching a value of ∼50° by the end of the simulation. We estimate a lower limit to the star formation efficiency (SFE) of 0.43. However, accounting for continued accretion from a massive disk and residual infall envelope, we estimate that the final SFE may be as high as ∼0.7. We examine observable properties of the outflow, especially the evolution of the cavity's opening angle, total mass, and momentum flux, and the velocity distributions of the outflowing gas, and compare with the massive protostars G35.20-0.74N and G339.88-1.26 observed by the Atacama Large Millimeter/submillimeter Array (ALMA), yielding constraints on their intrinsic properties.
more »
« less
- PAR ID:
- 10407479
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 947
- Issue:
- 1
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 40
- Size(s):
- Article No. 40
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Protostellar disks are an ubiquitous part of the star formation process and the future sites of planet formation. As part of the Early Planet Formation in Embedded Disks large program, we present high angular resolution dust continuum (∼40 mas) and molecular line (∼150 mas) observations of the Class 0 protostar IRAS 15398–3359. The dust continuum is small, compact, and centrally peaked, while more extended dust structures are found in the outflow directions. We perform a 2D Gaussian fitting and find the deconvolved size and 2σradius of the dust disk to be 4.5 × 2.8 au and 3.8 au, respectively. We estimate the gas+dust disk mass assuming optically thin continuum emission to be 0.6MJ–1.8MJ, indicating a very low mass disk. The CO isotopologues trace components of the outflows and inner envelope, while SO traces a compact, rotating disk-like component. Using several rotation curve fittings on the position–velocity diagram of the SO emission, the lower limits of the protostellar mass and gas disk radius are 0.022M⊙and 31.2 au, respectively, from our Modified 2 single power-law fitting. A conservative upper limit of the protostellar mass is inferred to be 0.1M⊙. The protostellar mass accretion rate and the specific angular momentum at the protostellar disk edge are found to be in the range of (1.3–6.1) × 10−6M⊙yr−1and (1.2–3.8) × 10−4km s−1pc, respectively, with an age estimated between 0.4 × 104yr and 7.5 × 104yr. At this young age with no clear substructures in the disk, planet formation would likely not yet have started. This study highlights the importance of high-resolution observations and systematic fitting procedures when deriving dynamical properties of deeply embedded Class 0 protostars.more » « less
-
Abstract We present Stratospheric Observatory For Infrared Astronomy (SOFIA) + Atacama Large Millimeter/submillimeter Array (ALMA) continuum and spectral-line polarization data on the massive molecular cloud BYF 73, revealing important details about the magnetic field morphology, gas structures, and energetics in this unusual massive star formation laboratory. The 154μm HAWC+ polarization map finds a highly organized magnetic field in the densest, inner 0.55 × 0.40 pc portion of the cloud, compared to an unremarkable morphology in the cloud’s outer layers. The 3 mm continuum ALMA polarization data reveal several more structures in the inner domain, including a parsec-long, ∼500M⊙“Streamer” around the central massive protostellar object MIR 2, with magnetic fields mostly parallel to the east–west Streamer but oriented north–south across MIR 2. The magnetic field orientation changes from mostly parallel to the column density structures to mostly perpendicular, at thresholdsNcrit= 6.6 × 1026m−2,ncrit= 2.5 × 1011m−3, andBcrit= 42 ± 7 nT. ALMA also mapped Goldreich–Kylafis polarization in12CO across the cloud, which traces, in both total intensity and polarized flux, a powerful bipolar outflow from MIR 2 that interacts strongly with the Streamer. The magnetic field is also strongly aligned along the outflow direction; energetically, it may dominate the outflow near MIR 2, comprising rare evidence for a magnetocentrifugal origin to such outflows. A portion of the Streamer may be in Keplerian rotation around MIR 2, implying a gravitating mass 1350 ± 50M⊙for the protostar+disk+envelope; alternatively, these kinematics can be explained by gas in free-fall toward a 950 ± 35M⊙object. The high accretion rate onto MIR 2 apparently occurs through the Streamer/disk, and could account for ∼33% of MIR 2's total luminosity via gravitational energy release.more » « less
-
Abstract We report high-resolution 1.3 mm continuum and molecular line observations of the massive protostar G28.20-0.05 with Atacama Large Millimeter/submillimeter Array. The continuum image reveals a ring-like structure with 2000 au radius, similar to morphology seen in archival 1.3 cm Very Large Array observations. Based on its spectral index and associated H30αemission, this structure mainly traces ionized gas. However, there is evidence for ∼30M⊙of dusty gas near the main millimeter continuum peak on one side of the ring, as well as in adjacent regions within 3000 au. A virial analysis on scales of ∼2000 au from hot core line emission yields a dynamical mass of ∼80M⊙. A strong velocity gradient in the H30αemission is evidence for a rotating, ionized disk wind, which drives a larger-scale molecular outflow. An infrared spectral energy distribution (SED) analysis indicates a current protostellar mass ofm*∼ 40M⊙forming from a core with initial massMc∼ 300M⊙in a clump with mass surface density of Σcl∼ 0.8 g cm−2. Thus the SED and other properties of the system can be understood in the context of core accretion models. A structure-finding analysis on the larger-scale continuum image indicates G28.20-0.05 is forming in a relatively isolated environment, with no other concentrated sources, i.e., protostellar cores, above ∼1M⊙found from ∼0.1 to 0.4 pc around the source. This implies that a massive star can form in relative isolation, and the dearth of other protostellar companions within the ∼1 pc environs is a strong constraint on massive star formation theories that predict the presence of a surrounding protocluster.more » « less
-
Abstract We present high-resolution high-sensitivity observations of the Class 0 protostar RCrA IRS5N as part of the Atacama Large Milimeter/submilimeter Array large program Early Planet Formation in Embedded Disks. The 1.3 mm continuum emission reveals a flattened continuum structure around IRS5N, consistent with a protostellar disk in the early phases of evolution. The continuum emission appears smooth and shows no substructures. However, a brightness asymmetry is observed along the minor axis of the disk, suggesting that the disk is optically and geometrically thick. We estimate the disk mass to be between 0.007 and 0.02M⊙. Furthermore, molecular emission has been detected from various species, including C18O (2–1),12CO (2–1),13CO (2–1), and H2CO (30,3− 20,2, 32,1− 22,0, and 32,2− 22,1). By conducting a position–velocity analysis of the C18O (2–1) emission, we find that the disk of IRS5N exhibits characteristics consistent with Keplerian rotation around a central protostar with a mass of approximately 0.3M⊙. Additionally, we observe dust continuum emission from the nearby binary source IRS5a/b. The emission in12CO toward IRS5a/b seems to emanate from IRS5b and flow into IRS5a, suggesting material transport between their mutual orbits. The lack of a detected outflow and large-scale negatives in12CO observed toward IRS5N suggests that much of the flux from IRS5N is being resolved out. Using a 1D radiative transfer model, we infer the mass of the envelope surrounding IRS5N to be ∼1.2M⊙. Due to this substantial surrounding envelope, the central IRS5N protostar is expected to be significantly more massive in the future.more » « less
