protostellar envelopes: a clue to the initial conditions of star formation

Bonnell, Ian A.; Bate, Matthew R.; Price, Nigel M.

doi:10.1093/mnras/279.1.121

Cited by 14 publications

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“…At the mean density calculated within r 0 (i.e. n H 2 ∼ 1 × 10 3 cm −3 ) and for T k = 20 K, the Jeans mass is M J 20 M (see Bonnell et al 1996, for a precise definition of M J ), which yields a Jeans mass number N J ∼ 10 for the flat inner core. In these simulations we also included turbulent fluctuations.…”

Section: Numerical Methods and Initial Conditionsmentioning

confidence: 99%

“…5 were taken at t ff −4×10 5 yr, t ff −2×10 5 yr, t ff −1.0×10 5 yr, and t ff − 0.4 × 10 5 yr, respectively. We can describe the evolution of the model clump as follows (see also Bonnell et al 1996;Inutsuka & Miyama 1997). Since the ellipsoidal clump initially contains several thermal Jeans masses (i.e.…”

Section: Numerical Methods and Initial Conditionsmentioning

confidence: 99%

“…This fast contraction proceeds until thermal and turbulent pressure gradients can stop the collapse along the minor axis, ensuring an approximate hydrostatic equilibrium in the (xy) plane (cf. Bonnell et al 1996).…”

Section: Numerical Methods and Initial Conditionsmentioning

confidence: 99%

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Probing the formation of intermediate- to high-mass stars in protoclusters

Peretto

Hennebelle

André

2006

A&A

110

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Aims. The earliest phases of massive star formation in clusters are still poorly understood. Here, we test the hypothesis for high-mass star formation proposed in our earlier paper (Peretto et al. 2006) stating that a massive, ultra-dense core may be currently forming at the center of the collapsing NGC 2264-C protocluster via the gravitational coalescence of several intermediate-mass Class 0 objects. Methods. In order to confirm the physical validity of this hypothesis, we carried out IRAM Plateau de Bure interferometer observations of NGC 2264-C and performed SPH numerical simulations of the collapse of a Jeans-unstable, prolate dense clump. A detailed comparison between these hydrodynamic simulations and both our earlier IRAM 30 m observations and the new interferometer observations is presented. Results. Our Plateau de Bure observations provide evidence for disk emission in three of the six Class 0-like objects identified earlier with the 30 m in the NGC 2264-C clump. Furthermore, they reveal the presence of a new compact source (C-MM13) located only ∼10 000 AU away, but separated by ∼1.1 km s −1 in (projected) velocity, from the most massive Class 0 object (C-MM3) lying at the very center of NGC 2264-C. Detailed comparison with our numerical SPH simulations supports the view that NGC 2264-C is an elongated cluster-forming clump in the process of collapsing and fragmenting along its long axis, leading to a strong dynamical interaction and possible protostar merger in the central region of the clump. The marked velocity difference observed between the two central objects C-MM3 and C-MM13, which can be reproduced in the simulations, is interpreted as an observational signature of this dynamical interaction. The present study also sets several quantitative constraints on the initial conditions of large-scale collapse in NGC 2264-C. Our hydrodynamic simulations indicate that the observed velocity pattern characterizes an early phase of protocluster collapse which survives for an only short period of time (i.e., ≤1 × 10 5 yr). To provide a good match to the observations the simulations require an initial ratio of turbulent to gravitational energy of only ∼5%, which strongly suggests that the NGC 2264-C clump is structured primarily by gravity rather than turbulence. The required "cold" initial conditions may result from rapid compression by an external trigger. Conclusions. We speculate that NGC 2264-C is not an isolated case but may point to key features of the initial phases of high-mass star formation in protoclusters.

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Section: Numerical Methods and Initial Conditionsmentioning

confidence: 99%

Section: Numerical Methods and Initial Conditionsmentioning

confidence: 99%

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Probing the formation of intermediate- to high-mass stars in protoclusters

Peretto

Hennebelle

André

2006

A&A

110

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“…Previous calculations of the isothermal collapse of prolate clouds not adhering to the Jeans condition, starting with either uniform-density profiles (Nelson & Papaloizou 1993) or Gaussian condensations (Boss 1993;Boss & Myhill 1995;Bonnell et al 1996;Sigalotti & Klapp 1997;Sigalotti 1998a), have predicted fragmentation into binary systems for a wide range of the initial conditions. In this paper we recalculate the isothermal collapse of prolate core models using high spatial resolution to discern whether they will still undergo fragmentation into a protostellar binary system or condense into a singularity without fragmenting.…”

Section: Introductionmentioning

confidence: 99%

Protostellar collapse models of prolate molecular cloud cores

Sigalotti¹,

Klapp²

2001

A&A

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Abstract. The continued detection of binary systems among pre-main-sequence stars suggests that fragmentation is a very frequent process during the early stages of star formation. However, the fragmentation hypothesis rests only upon the results of three-dimensional hydrodynamics code calculations. The validity of isothermal fragmentation calculations was questioned by the results of Truelove et al. (1997), and more recently, of Boss et al. (2000), who found, working at very high spatial resolution, that a particular Gaussian cloud model collapsed isothermally to form a singular filament rather than a binary or quadruple protostellar system as predicted by previous calculations. Sufficiently high spatial resolution is necessary to resolve the Jeans length and hence avoid artificial fragmentation in isothermal collapse calculations. Here we use an adaptive, spherical-coordinate hydrodynamics code based on the "zooming" coordinates to investigate the isothermal collapse of centrally condensed (Gaussian), prolate (2:1 axial ratio) cloud core models, with thermal energy α ≈ 0.22 and varied rotational energy (0.246 ≤ β ≤ 0.00025), to discern whether they will still undergo fragmentation into a protostellar binary system, as found in most previous prolate cloud collapse calculations, or condense all the way into a thin filament, as suggested by the linear analysis of Inutsuka & Miyama (1992) and the findings of Truelove et al. and Boss et al. for the spherical, Gaussian cloud model. The prolate clouds all collapsed self-similarly to produce an intermediate barlike core, which then shrank indefinetely into a singular filament without fragmenting. Collapse of the bar into a thin filament also occurred self-similarly, with the forming filaments being much longer than the Jeans length. Since the filaments form at maximum densities that are typical of the transition from the isothermal to the nonisothermal phase, gradual heating may retard the collapse and allow fragmentation of the filament into a binary or multiple protostellar core, as required to explain the high frequency of binary stars.

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“…Finally, recent studies of velocity gradients in dense cores and their environs indicate that the cores appear to spin independently of their surroundings, with inferred ratios of their rotational to their gravitational energy b in the range between 0.001 and 0.03 . Paralleling these observational advances, numerical calculations of the collapse and fragmentation of prolate cloud cores, with either uniform-density proÐles (Nelson & Papaloizou 1993) or Gaussian condensations (Boss 1993b ;Boss & Myhill 1995 ;Bonnell, Bate, & Price 1996 ;Sigalotti & Klapp 1997, hereafter SK ;Sigalotti 1998a), have shown that cloud cores of prolate shape are quite propense to fragment into protostellar binary systems for a wide range of the initial parameter space (a, b), where a and b denote, respectively, the ratio of the thermal and rotational to the absolute value of the gravitational energy. None of these calculations have, however, included the e †ects of magnetic Ðelds, and so they apply only to collapsing cloud cores for which ambipolar di †usion has had enough time to lessen the magnetic forces.…”

Section: Introductionmentioning

confidence: 99%

Collapse and Fragmentation Models of Tidally Interacting Molecular Cloud Cores. IV. Initial Slow Rotation and Magnetic Field Support

Sigalotti¹,

Klapp²

2000

ApJ

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Fragmentation has long been advocated as the primary mechanism for explaining the observed binary frequency among preÈmain-sequence stars and, more recently, for explaining the emerging evidence for binary and multiple protostellar systems. The role of magnetic Ðelds and ambipolar di †usion is essential to understand how dense cloud cores begin dynamic collapse and eventually fragment into protostars. Here we consider new numerical models of the gravitational collapse and fragmentation of slowly rotating molecular cloud cores, including the e †ects of magnetic support and ambipolar di †usion. The starting point of the evolution is provided by a magnetically stable (subcritical) condensation that results from adding a magnetic Ðeld pressure, B2/8n [with the Ðeld strength given by the scaling relation B \ to a reference state consisting of a thermally supercritical (a B 0.36), slowly rotatingGaussian cloud core of prolate shape and central densityThe e †ects of ambipolar di †u-o 0 . sion are approximated by allowing the reference Ðeld strength to gradually decrease over a timescale B 0 of 10 free-fall times. The models also include the e †ects of tidal interaction due to a gravitational encounter with another protostar, and so they may apply to low-mass star formation within a clusterforming environment. The results indicate that the magnetic forces delay the onset of dynamic collapse, and hence of fragmentation, by an amount of time that depends on the initial central mass-to-Ñux ratio. Compared with previous magnetic collapse calculations of rapidly rotating (b \ 0.12) clouds, lower initial rotation (b B 0.037) is seen to result in much shorter delay periods, thus anticipating binary fragmentation. In general, the results show that the models are still susceptible to fragment into binary systems. Intermediate magnetic support (g B 0.285) and low tidal forces may lead to Ðnal (q [ 0.201) triple or quadruple protostellar systems, while increasing the size of g and q always results in Ðnal binary protostellar cores. The formed binary systems have separations of B200È350 AU, suggesting that the recently observed peaks around B90 AU and 215 AU for T Tauri stars may be explained by the collapse and fragmentation of initially slowly rotating magnetic cloud cores with b [ 0.04.

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protostellar envelopes: a clue to the initial conditions of star formation

Cited by 14 publications

References 0 publications

Probing the formation of intermediate- to high-mass stars in protoclusters

Probing the formation of intermediate- to high-mass stars in protoclusters

Protostellar collapse models of prolate molecular cloud cores

Collapse and Fragmentation Models of Tidally Interacting Molecular Cloud Cores. IV. Initial Slow Rotation and Magnetic Field Support

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