On the reliability of protostellar disc mass measurements and the existence of fragmenting discs

Dunham, Michael M.; Vorobyov, Eduard I.; Arce, Héctor G.

doi:10.1093/mnras/stu1511

Cited by 68 publications

(80 citation statements)

References 75 publications

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“…E.g., for our baseline solar-type model, there are 20 accretion episodes, each of which has a f bin /20 ≈ 1.5% chance of forming a new companion. The accretion rates and stochastic variability of embedded Class 0 protostars are higher than their older Class I counterparts (Froebrich et al 2006;Krumholz et al 2009;Peters et al 2010;Dunham et al 2014;Hartmann et al 2016), and so fragmentation may preferentially occur during earlier episodes. To encompass this possibility, we consider a model Frag1 in which the probability of fragmentation is p ∝ t −0.5 , i.e., the first accretion episode at t = 0.1 is three times more likely to form a new companion than the last episode.…”

Section: Initial Conditionsmentioning

confidence: 99%

Formation of close binaries by disc fragmentation and migration, and its statistical modelling

Tokovinin

Moe

2019

Monthly Notices of the Royal Astronomical Society

129

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Joint statistics of periods and mass ratios of close binaries and its dependence on primary mass can be explained by assuming that seed binary companions are formed by disc fragmentation at random intervals during assemblage of stellar mass and migrate inwards as they accrete from the circumbinary disk. A toy model based on simple prescriptions for the companion growth and migration reproduces such aspects of close solar-mass binaries as the distribution of binary periods P , the brown dwarf desert at short P , the nearly uniform distribution of mass ratios, and a population of equal-mass binaries (twins) that decreases linearly in frequency with log P . For massive stars, the model predicts a large fraction of early mergers, a distribution of log P with a negative slope, and a mass-ratio distribution that is also uniform but with a substantially reduced twin fraction. By treating disc fragmentation as a stochastic process, we also reproduce the observed properties of compact triples. Success of our toy model suggests that most close binaries and compact triples indeed formed by disc fragmentation followed by accretion-driven inward migration.

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Section: Initial Conditionsmentioning

confidence: 99%

Formation of close binaries by disc fragmentation and migration, and its statistical modelling

Tokovinin

Moe

2019

Monthly Notices of the Royal Astronomical Society

129

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“…The mass is calculated using the flux of the Gaussian and point source, i.e., F ps + F G , and assumes an average temperature of 30 K. This temperature could be lower, which would increase the mass (e.g., Jørgensen et al 2009;Dunham et al 2014) 3.3. Power-law disk…”

Section: Gaussian Intensity Distributionmentioning

confidence: 99%

Constraining the physical structure of the inner few 100 AU scales of deeply embedded low-mass protostars

Persson

Harsono

Tobin

et al. 2016

A&A

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Context. The physical structure of deeply embedded low-mass protostars (Class 0) on scales of less than 300 AU is still poorly constrained. While molecular line observations demonstrate the presence of disks with Keplerian rotation toward a handful of sources, others show no hint of rotation. Determining the structure on small scales (a few 100 AU) is crucial for understanding the physical and chemical evolution from cores to disks. Aims. We determine the presence and characteristics of compact, disk-like structures in deeply embedded low-mass protostars. A related goal is investigating how the derived structure affects the determination of gas-phase molecular abundances on hot-core scales. Methods. Two models of the emission, a Gaussian disk intensity distribution and a parametrized power-law disk model, are fitted to subarcsecond resolution interferometric continuum observations of five Class 0 sources, including one source with a confirmed Keplerian disk. Prior to fitting the models to the de-projected real visibilities, the estimated envelope from an independent model and any companion sources are subtracted. For reference, a spherically symmetric single power-law envelope is fitted to the larger scale emission (∼1000 AU) and investigated further for one of the sources on smaller scales. Results. The radii of the fitted disk-like structures range from ∼90−170 AU, and the derived masses depend on the method. Using the Gaussian disk model results in masses of 54−556 × 10 −3 M , and using the power-law disk model gives 9−140 × 10 −3 M . While the disk radii agree with previous estimates the masses are different for some of the sources studied. Assuming a typical temperature distribution (r −0.5 ), the fractional amount of mass in the disk above 100 K varies from 7% to 30%. Conclusions. A thin disk model can approximate the emission and physical structure in the inner few 100 AU scales of the studied deeply embedded low-mass protostars and paves the way for analysis of a larger sample with ALMA. Kinematic data are needed to determine the presence of any Keplerian disk. Using previous observations of p-H 18 2 O, we estimate the relative gas phase water abundances relative to total warm H 2 to be 6.2 × 10 −5 (IRAS 2A), 0.33 × 10 −5 (IRAS 4A-NW), 1.8 × 10 −7 (IRAS 4B), and <2 × 10 −7 (IRAS 4A-SE), roughly an order of magnitude higher than previously inferred when both warm and cold H 2 were used as reference. A spherically symmetric single power-law envelope model fails to simultaneously reproduce both the small-and large-scale emission.

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“…Nevertheless, a lower value of Σ cr = 0.1 g cm −2 results only in a few percent increase in the net disk mass (see Fig. 2 in Dunham et al 2014a). We found that our algorithm generally works well, but may somewhat overestimate the disk mass in the early Class 0 stage (when the inner part of the infalling envelope may have densities exceeding Σ cr ) and somewhat underestimate the disk mass in the late Class I and Class II stages (when the disk spreads out and its density drops below Σ cr in the outer parts).…”

Section: Comparison Of Disk Propertiesmentioning

confidence: 99%

The effect of external environment on the evolution of protostellar disks

Vorobyov

Lin

Guêdel

2014

A&A

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Aims. Using numerical hydrodynamics simulations, we studied the gravitational collapse of prestellar cores of subsolar mass embedded into a low-density external environment. Methods. Four models with different magnitude and direction of rotation of the external environment with respect to the central core were studied and compared with an isolated model. Results. We found that the infall of matter from the external environment can significantly alter the disk properties as compared to those seen in the isolated model. Depending on the magnitude and direction of rotation of the external environment, a variety of disks can form including compact (≤200 AU) ones shrinking in size owing to infall of external matter with low angular momentum, as well as extended disks forming from infall of external matter with high angular momentum. The former are usually stable against gravitational fragmentation, while the latter are prone to fragmentation and formation of stellar systems with substellar/very-low-mass companions. In the case of a counter-rotating external environment, very compact (<5 AU) and short-lived ( < ∼ a few 10 5 yr) disks can form when infalling material has low angular momentum. The most interesting case is found for the infall of counter-rotating external material with high angular momentum, leading to the formation of counter-rotating inner and outer disks separated by a deep gap at a few tens AU. The gap migrates inward owing to accretion of the inner disk onto the protostar, turns into a central hole, and finally disappears, giving way to the outer strongly gravitationally unstable disk. This model may lead to the emergence of a transient stellar system with planetary/substellar components counter-rotating with respect to that of the star.

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On the reliability of protostellar disc mass measurements and the existence of fragmenting discs

Cited by 68 publications

References 75 publications

Formation of close binaries by disc fragmentation and migration, and its statistical modelling

Formation of close binaries by disc fragmentation and migration, and its statistical modelling

Constraining the physical structure of the inner few 100 AU scales of deeply embedded low-mass protostars

The effect of external environment on the evolution of protostellar disks

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