Neutral stellar winds that drive bipolar outflows in low-mass protostars

Lizano, Susana; Heiles, C.; Rodrı́guez, Luis F.; Koo, Bon‐Chul; Shu, Frank H.; Hasegawa, Takashi; Hayashi, Saeko S.; Mirabel, I. F.

doi:10.1086/166335

Cited by 80 publications

(59 citation statements)

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“…Observations of neutral atomic winds from protostars show outflow velocities of roughly this value (Lizano et al 1988, Giovanardi et al 2000. The total energy input from protostellar winds will substantially exceed the amount that can be transferred to the turbulence because of radiative cooling at the wind termination shock.…”

Section: Protostellar Outflowsmentioning

confidence: 99%

“…We can estimate their average energy input rate into the overall ISM, following McKee (1989), by assuming that some fraction f w of the mass accreted onto a star during its formation is expelled in a wind travelling at roughly the escape velocity. Shu et al (1988) argue that f w ≈ 0.4, and that most of the mass is ejected from close to the stellar surface, where the escape velocity…”

Section: Protostellar Outflowsmentioning

confidence: 99%

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Control of star formation by supersonic turbulence

2004

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Understanding the formation of stars in galaxies is central to much of modern astrophysics. However, a quantitative prediction of the star formation rate and the initial distribution of stellar masses remains elusive. For several decades it has been thought that the star formation process is primarily controlled by the interplay between gravity and magnetostatic support, modulated by neutral-ion drift (known as ambipolar diffusion in astrophysics). Recently, however, both observational and numerical work has begun to suggest that supersonic turbulent flows rather than static magnetic fields control star formation. To some extent, this represents a return to ideas popular before the importance of magnetic fields to the interstellar gas was fully appreciated. This review gives a historical overview of the successes and problems of both the classical dynamical theory, and the standard theory of magnetostatic support from both observational and theoretical perspectives. The outline of a new theory relying on control by driven supersonic turbulence is then presented. Numerical models demonstrate that although supersonic turbulence can provide global support, it nevertheless produces density enhancements that allow local collapse. Inefficient, isolated star formation is a hallmark of turbulent support, while efficient, clustered star formation occurs in its absence. The consequences of this theory are then explored for both local star formation and galactic scale star formation. It suggests that individual star-forming cores are likely not quasi-static objects, but dynamically collapsing. Accretion onto these objects varies depending on the properties of the surrounding turbulent flow; numerical models agree with observations showing decreasing rates. The initial mass distribution of stars may also be determined by the turbulent flow. Molecular clouds appear to be transient objects forming and dissolving in the larger-scale turbulent flow, or else quickly collapsing into regions of violent star formation. We suggest that global star formation in galaxies is controlled by the same balance between gravity and turbulence as small-scale star formation, although modulated by cooling and differential rotation. The dominant driving mechanism in star-forming regions of galaxies appears to be supernovae, while elsewhere coupling of rotation to the gas through magnetic fields or gravity may be important.

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Section: Protostellar Outflowsmentioning

confidence: 99%

Section: Protostellar Outflowsmentioning

confidence: 99%

Control of star formation by supersonic turbulence

2004

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“…in [Fe ii] are increasingly frequent (see Bally et al 2007, for a review). Atomic jets differ by their high speed and collimation from the "neutral atomic outflows" detected in H i in a few young protostars, whose bulk mass is moving at ≤20 km s −1 (Lizano et al 1988; Rodriguez et al 1990). …”

Section: Introductionmentioning

confidence: 98%

Molecule survival in magnetized protostellar disk winds

Panoglou¹,

Cabrit²,

Forêts³

et al. 2012

A&A

103

144

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Context. Molecular counterparts to atomic jets have recently been detected within 1000 AU of young stars at early evolutionary stages. Reproducing these counterparts is an important new challenge for proposed ejection models. Aims. We explore whether molecules may survive in the magneto-hydrodynamic (MHD) disk wind solution currently invoked to reproduce the kinematics and tentative rotation signatures of atomic jets in T Tauri stars. Methods. The coupled ionization, chemical, and thermal evolution along dusty flow streamlines is computed for the prescribed MHD disk wind solution, using a method developed for magnetized shocks in the interstellar medium. Irradiation by (wind-attenuated) coronal X-rays and far-ultraviolet photons from accretion hot spots is included, with an approximate self-shielding of H 2 and CO. Disk accretion rates of 5 × 10 −6 , 10 −6 and 10 −7 M yr −1 are considered, representative of low-mass young protostars (so-called "Class 0"), evolved protostars ("Class I") and very active T Tauri stars ("Class II") respectively. Results. The disk wind has an "onion-like" thermo-chemical structure, with streamlines launched from larger radii having lower temperature and ionization, and higher H 2 abundance. The coupling between charged and neutral fluids is sufficient to eject molecules from the disk out to at least 9 AU. The launch radius beyond which most H 2 survives moves outward with evolutionary stage, from 0.2 AU (sublimation radius) in the Class 0 disk wind, to 1 AU in the Class I, and >1 AU in the Class II. In this molecular wind region, CO survives in the Class 0 but is significantly photodissociated in the Class I/II. Balance between ambipolar heating and molecular cooling establishes a moderate asymptotic temperature 700−3000 K, with cooler jets at earlier protostellar stages. As a result, endothermic formation of H 2 O is efficient, with abundances up to 10 −4 , while CH + and SH + can reach ≥10 −6 in the hotter and more ionised Class I/II winds. Conclusions. A centrifugal MHD disk wind launched from beyond 0.2−1 AU can produce molecular jets/winds up to speeds 100 km s −1 in young low-mass stars ranging from Class 0 to active Class II. The model predicts a high abundance ratio of H 2 to CO and an increase of molecular launch radius, temperature, and flow width as the source evolves, in promising agreement with current observed trends. Calculations of synthetic maps and line profiles in H 2 , CO and H 2 O will allow detailed tests of the model against observations.

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“…Molecular outflows show various characteristics such as radio and optical jets, atomic hydrogen stellar wind, molecular hydrogen jets and interstellar masers. The stars eject mass in energetic flows during formation (Lada 1985;Lizano et al 1988;Natta et al 1988;Lane 1989;Felli et al 1992;Russell et al 1992;Matzner & Mckee 1999;Bally et al 2001;Reipurth et al 2002). In the 1990s, progress was made in observing and understanding the collapse of protostars (Zhou 1992;Evans 1999;Myers et al 1996).…”

Section: Introductionmentioning

confidence: 99%

A study of high velocity molecular outflows with an up-to-date sample

Wu¹,

Wei²,

Zhao³

et al. 2004

A&A

290

291

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Abstract.A statistical study of the properties of molecular outflows is performed based on an up-to-date sample. 391 outflows were identified in published articles or preprints before February 28, 2003. The parameters of position, morphology, mass, energy, outflow dynamics and central source luminosity are presented for each outflow source. Outflow lobe polarity is known for all the sources, and 84% are found to be bipolar. The sources are divided into low mass and high mass groups according to either the available bolometric luminosity of the central source or the outflow mass. The pace of discovery of outflows over the past seven years has increased much more rapidly than in previous periods. Surveys for outflows are still continuing. The number of high-mass outflows detected (139) has considerably increased, showing that they are commonly associated with massive as well as low mass stars. Energetic mass ejection may be a common aspect of the formation of high mass as well as low mass stars. Outflow masses are correlated strongly with bolometric luminosity of the center sources, which was obtained for the first time. There are also correlations between the central source luminosity and the parameters of mechanical luminosity and the thrust or force necessary to drive the outflow. The results show that flow mass, momentum and energy depend on the nature of the central source. Despite their similarity, there are differences between the high mass and low mass outflows. Low mass outflows are more collimated than high mass outflows. On average, the mass of high mass sources can be more than two orders of magnitude larger than those of low mass outflows. The relation between flow mass and dynamical time appears to differ for the two types of outflows. Low mass sources make up 90% of outflows associated with HH objects while high mass outflows make up 61% of the sources associated with H 2 O masers. Sources with characteristics of collapse or infall comprise 12% of the entire outflow sample. The spatial distribution of the outflow sources in the Galaxy is presented and the local occurrence rate is compared with the stellar birth rate.

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Neutral stellar winds that drive bipolar outflows in low-mass protostars

Cited by 80 publications

References 0 publications

Control of star formation by supersonic turbulence

Control of star formation by supersonic turbulence

Molecule survival in magnetized protostellar disk winds

A study of high velocity molecular outflows with an up-to-date sample

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