The Initial Conditions for Formation of Low‐Mass Stars: Kinematics and Density Structure of the Protostellar Envelope in B335

Saito, Masao; Sunada, Kazuyoshi; Kawabe, Ryohei; Kitamura, Yoshihisa; Hirano, Naomi

doi:10.1086/307244

Cited by 45 publications

(89 citation statements)

References 30 publications

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“…C (1−0) interferometric observations have traced the rotational infalling motion of the envelope from radii of ∼20 000 down to ∼1000 au. No clear rotational motion is detected on 100-500 au scales (Saito et al 1999;Harvey et al 2003;Yen et al 2011) and the central circumstellar disk radius is estimated to be smaller than 100 au. Our SMA observations.…”

Section: Discussionmentioning

confidence: 94%

“…On the contrary, sources that show an alignment between the B direction and the outflow direction (e.g., L1157, B335, SVS13-B, and L1448C) have been studied with ALMA or the NOrthern Extended Millimeter Array (NOEMA) highresolution observations and stand as robust single protostars at envelope scales of ∼5000-10000 au. No large disk has been detected so far in these sources (Saito et al 1999;Yen et al 2010;Chiang et al 2012;Tobin et al 2015) while L1448N-B for instance was suggested recently to harbor a large disk encompassing several multiple sources at scales ∼100 au . These results support those of Zhang et al (2014): the possible link between fragmentation and magnetic field topology points toward a less efficient magnetic braking and redistribution of angular momentum when the B-field is misaligned.…”

Section: A B−o < 45mentioning

confidence: 94%

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SMA observations of polarized dust emission in solar-type Class 0 protostars: Magnetic field properties at envelope scales

Galametz

Maury

Girart

et al. 2018

A&A

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Aims. Although from a theoretical point of view magnetic fields are believed to play a significant role during the early stages of star formation, especially during the main accretion phase, the magnetic field strength and topology is poorly constrained in the youngest accreting Class 0 protostars that lead to the formation of solar-type stars. Methods. We carried out observations of the polarized dust continuum emission with the SMA interferometer at 0.87 mm to probe the structure of the magnetic field in a sample of 12 low-mass Class 0 envelopes in nearby clouds, including both single protostars and multiple systems. Our SMA observations probed the envelope emission at scales ∼600 − 5000 au with a spatial resolution ranging from 600 to 1500 au depending on the source distance. Results. We report the detection of linearly polarized dust continuum emission in all of our targets with average polarization fractions ranging from 2% to 10% in these protostellar envelopes. The polarization fraction decreases with the continuum flux density, which translates into a decrease with the H 2 column density within an individual envelope. Our analysis show that the envelope-scale magnetic field is preferentially observed either aligned or perpendicular to the outflow direction. Interestingly, our results suggest for the first time a relation between the orientation of the magnetic field and the rotational energy of envelopes, with a larger occurrence of misalignment in sources in which strong rotational motions are detected at hundreds to thousands of au scales. We also show that the best agreement between the magnetic field and outflow orientation is found in sources showing no small-scale multiplicity and no large disks at ∼100 au scales.

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Section: Discussionmentioning

confidence: 94%

Section: A B−o < 45mentioning

confidence: 94%

SMA observations of polarized dust emission in solar-type Class 0 protostars: Magnetic field properties at envelope scales

Galametz

Maury

Girart

et al. 2018

A&A

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“…The central star mass is ∼ 0.05M⊙. The large-scale rotation velocity of B335 is obtained from single-dish observations (Saito et al 1999;Yen, Takakuwa & Ohashi 2011;Kurono et al 2013). Based on these observations, the initial rotational velocity of B335 is assumed to be a rigid-body rotation with an angular velocity of 0.8 km s −1 pc −1 .…”

Section: B335mentioning

confidence: 99%

The origin of rotation profiles in star-forming clouds

Takahashi

Tomida

Machida

et al. 2016

Mon. Not. R. Astron. Soc.

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Angular momentum distribution and its redistribution are of crucial importance in the formation and evolution of circumstellar disks. Many molecular line observations toward young stellar objects indicate that radial distributions of the specific angular momentum j have a characteristic profile. In the inner region, typically R < ∼ 100 AU, the specific angular momenta distribute like j ∝ r 1/2 , indicating existence of rotationally supported disk. In outer regions, R > ∼ 5000 AU, j increases as the radius increases and the slope is steeper than unity, which is supposed to reflect the original angular momentum distributions in the maternal molecular clouds. In the intermediate region, 100 AU < ∼ R < ∼ 5000AU, j-distribution appears almost flat. While this is often interpreted as a consequence of conservation of the specific angular momentum, the interpretation actually is insufficient and requires a stronger condition that the initial distribution of j must be spatially uniform. However, this requirement seems to be unrealistic and inconsistent with observations. In this work, we propose a simple alternative explanation; the apparently flat j profile is produced by strong elongation due to the large velocity gradient in the accreting flow no matter what the initial j distribution is. To show this we provide a simple analytic model for gravitational collapse of molecular clouds. We also propose a method to estimate ages of protostars using solely the observed rotation profile. We demonstrate its validity in comparison with hydrodynamic simulations, and apply the model to young stellar objects such as L1527 IRS, TMC-1A and B335.

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“…An additional compact component of CS emission ap-J p 5-4 pears coincident with the continuum peak, with a more limited velocity extent than found in the two lobes. Each lobe exhibits emission at velocities both redshifted and blueshifted from the systemic velocity of 8.3 km s (Hirano et al 1992;Chandler & Sargent 1993;Choi et al 1999;Saito et al 1999). No velocity gradient is evident in the central concentration that might be associated with the rotation axis inferred at larger scales (Frerking, Langer, & Wilson 1987;Zhou 1995).…”

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confidence: 91%

Small-Scale Structure of the Protostellar Collapse Candidate B335 Imaged in CS [ITAL]J[/ITAL] = 5–4 Emission

Wilner

Myers

Mardones

et al. 2000

The Astrophysical Journal

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We present interferometer observations of CS emission in B335, an isolated round globule generally J p 5-4 recognized from single-dish spectral line mapping to be the best candidate for a collapsing protostar. The images, with ∼2Љ .5 (0.003 pc) spatial resolution and 0.13 km s Ϫ1 velocity resolution, show complex structure in the purported infall zone. The emission is dominated by a clumpy conical structure oriented in the east-west direction that we identify with a slow, dense component of the bipolar flow visible on larger size scales. Comparison with the detailed predictions of the inside-out collapse model previously derived from single-dish observations show important discrepancies. The high-resolution CS images show no evidence for infalling material at J p 5-4 velocities greater than 0.5 km s Ϫ1 coincident with the protostar that corresponds to emission in the wings of the single-dish spectrum. Instead, the emission at velocities expected for collapse is found to be associated with the outflow lobes, offset from the protostar position. Depletion may diminish the signal from infall of the densest gas. Bright clumps at blueshifted velocities within the outflow may contribute to the asymmetric appearance of optically thick lines observed with beam sizes too large to resolve these small-scale structures.

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The Initial Conditions for Formation of Low‐Mass Stars: Kinematics and Density Structure of the Protostellar Envelope in B335

Cited by 45 publications

References 30 publications

SMA observations of polarized dust emission in solar-type Class 0 protostars: Magnetic field properties at envelope scales

SMA observations of polarized dust emission in solar-type Class 0 protostars: Magnetic field properties at envelope scales

The origin of rotation profiles in star-forming clouds

Small-Scale Structure of the Protostellar Collapse Candidate B335 Imaged in CS [ITAL]J[/ITAL] = 5–4 Emission

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