scholarly journals Magnetohydrodynamic Origin of Jets from Accretion Disks

1999 ◽  
Vol 194 ◽  
pp. 208-218 ◽  
Author(s):  
R.V.E. Lovelace ◽  
G.V. Ustyugova ◽  
A.V. Koldoba
Keyword(s):  
Accretion Disks ◽  
Mass Flux ◽  
Compact Stars ◽  
Young Stellar Objects ◽  
Region Of Origin ◽  
Stellar Objects ◽  
New Developments ◽  
Poynting Flux ◽  
Radio Jets ◽  
Astrophysical Objects

A review is made of recent magnetohydrodynamic (MHD) theory and simulations of origin of jets from accretion disks. Many compact astrophysical objects emit powerful, highly-collimated, oppositely directed jets. Included are the extra galactic radio jets of active galaxies and quasars, and old compact stars in binaries, and emission line jets in young stellar objects. It is widely thought that these different jets arise from rotating, conducting accretion disks threaded by an ordered magnetic field. The twisting of the B field by the rotation of the disk drives the jets by magnetically extracting matter, angular momentum, and energy from the accretion disk. Two main regimes have been discussed theoretically, hydromagnetic winds which have a significant mass flux, and Poynting flux jets where the mass flux is negligible. Over the past several years, exciting new developments on models of jets have come from progress in MHD simulations which now allow the study of the origin -the acceleration and collimation - of jets from accretion disks. Simulation studies in the hydromagnetic wind regime indicate that the outflows are accelerated close to their region of origin whereas the collimation occurs at much larger distances.

scholarly journals Models of Accretion Disks Around Young Stars

2004 ◽  
Vol 221 ◽  
pp. 403-410 ◽  
Author(s):  
Paola D'Alessio ◽  
Nuria Calvet ◽  
Lee Hartmann ◽  
James Muzerolle ◽  
Michael Sitko
Keyword(s):  
Accretion Disks ◽  
Young Stars ◽  
Stellar Surface ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Disk Structure ◽  
Accretion Rates ◽  
Accretion Shocks

We discuss the importance of accretion in calculating disk models for young stellar objects. In particular, we show that a disk inner rim, irradiated by both the star and the accretion shocks at the stellar surface, can naturally explain recent observations of DG Tau with the Keck interferometer. We present models for two objects, with mass accretion rates differing by almost two orders of magnitude, to illustrate the effects of accretion on the overall disk structure and emission.

scholarly journals Episodic accretion in focus: revealing the environment of FU Orionis-type stars

2018 ◽  
Vol 14 (S345) ◽  
pp. 87-90
Author(s):  
O. Fehér ◽  
Á. Kóspál ◽  
P. Ábrahám ◽  
M. R. Hogerheijde ◽  
Ch. Brinch ◽  
...  
Keyword(s):  
Accretion Disks ◽  
Accretion Rate ◽  
Central Star ◽  
Systematic Investigation ◽  
Young Stars ◽  
Young Stellar Objects ◽  
Circumstellar Disk ◽  
Stellar Objects ◽  
Evolutionary Phase ◽  
Intense Mass

AbstractThe earliest phases of star formation are characterised by intense mass accretion from the circumstellar disk to the central star. One group of young stellar objects, the FU Orionis-type stars exhibit accretion rate peaks accompanied by bright eruptions. The occurance of these outbursts might solve the luminosity problem of protostars, play a key role in accumulating the final star mass, and have a significant effect on the parameters of the envelope and the disk. In the framework of the Structured Accretion Disks ERC project, we are conducting a systematic investigation of these sources with millimeter interferometry to examine whether they represent normal young stars in exceptional times or they are unusual objects. Our results show that FU Orionis-type stars can be similar to both Class I and Class II systems and may be in a special evolutionary phase between the two classes with their infall-driven episodic eruptions being the main driving force of the transition.

Heating mechanisms in accretion disks around young stellar objects

2018 ◽  
Vol 14 (S345) ◽  
pp. 255-256
Author(s):  
Natália F.S. Andrade ◽  
Rafael Rechiche de Campos ◽  
Vera Jatenco-Pereira
Keyword(s):  
Accretion Disks ◽  
Alfven Waves ◽  
Young Stellar Objects ◽  
Alfvén Waves ◽  
Rotational Instability ◽  
Mhd Turbulence ◽  
Stellar Objects ◽  
Heating Source ◽  
Order Of Magnitude ◽  
Magnetic Filed

AbstractAccretion disks are observed around young stellar objects such as T Tauri stars. In order to complete the star formation, particles in the disk need to loose angular momentum in order to be accreted into the central object. The magneto-rotational instability (MRI) is probably the mechanism responsible for a magneto-hydrodynamic (MHD) turbulence that leads to disk accretion, which implies the disk particles to be coupled with the magnetic filed lines. As the temperature in the disk is low, we considered, besides the viscous heating mechanism often included in the models by means of the α - prescription, the damping of Alfvén waves as an additional heating source. In particular, we show that the mechanism derived that couples the turbulent and non-linear damping mechanisms of Alfvén waves proved to be very efficient, generating temperatures almost one order of magnitude higher than those mechanisms considered independently.

scholarly journals Massive Star Formation: Observational Constraints

1997 ◽  
Vol 182 ◽  
pp. 525-536
Author(s):  
Ed Churchwell
Keyword(s):  
Star Formation ◽  
Accretion Disks ◽  
Massive Star ◽  
Young Stellar Objects ◽  
Mass Star ◽  
Structure And Properties ◽  
Low Mass Stars ◽  
Stellar Objects ◽  
The Past ◽  
Low Mass

Observations during the past several years strongly imply that virtually every star, independent of final mass, goes through a phase of rapid outflow simultaneously with rapid accretion during formation. The structure and properties of outflows and accretion disks associated with low-mass star formation has received intensive observational attention during the past several years (see the reviews and references in Lada 1985; Edwards, Ray, and Mundt 1993; Fukui et al. 1993; and this symposium). Young stellar objects (YSOs) with Lbol < 103 L⊘ will be referred to as “low-mass” stars in this review. The range of physical properties of CO outflows associated with YSOs of all masses are enormous, see Fukui et al. (1993). I will focus attention in this review on what we know about massive YSOs and their environments.

scholarly journals Radio jets from young stellar objects

2018 ◽  
Vol 26 (1) ◽  
Author(s):  
Guillem Anglada ◽  
Luis F. Rodríguez ◽  
Carlos Carrasco-González
Keyword(s):  
Young Stellar Objects ◽  
Stellar Objects ◽  
Radio Jets

scholarly journals A study of radial self-similar non-relativistic MHD outflow models: parameter space exploration and application to the water fountain W43A

2020 ◽  
Vol 501 (2) ◽  
pp. 2071-2090
Author(s):  
C Ceccobello ◽  
M H M Heemskerk ◽  
Y Cavecchi ◽  
W H T Vlemmings ◽  
D Tafoya
Keyword(s):  
Young Stellar Objects ◽  
Parameter Study ◽  
Rotating Disc ◽  
Stellar Objects ◽  
Global Properties ◽  
Wide Range ◽  
Astrophysical Objects ◽  
Self Similar ◽  
Water Maser

ABSTRACT Outflows, spanning a wide range of dynamical properties and spatial extensions, have now been associated with a variety of accreting astrophysical objects, from supermassive black holes at the core of active galaxies to young stellar objects. The role of such outflows is key to the evolution of the system that generates them, for they extract a fraction of the orbiting material and angular momentum from the region close to the central object and release them in the surroundings. The details of the launching mechanism and their impact on the environment are fundamental to understand the evolution of individual sources and the similarities between different types of outflow-launching systems. We solve semi-analytically the non-relativistic, ideal, magnetohydrodynamics equations describing outflows launched from a rotating disc threaded with magnetic fields using our new numerical scheme. We present here a parameter study of a large sample of new solutions. We study the different combinations of forces that lead to a successfully launched jet and discuss their global properties. We show how these solutions can be applied to the outflow of the water fountain W43A for which we have observational constraints on magnetic field, density and velocity of the flow at the location of two symmetrical water maser emitting regions.

scholarly journals A movie of accretion/ejection of material in a high-mass YSO in Orion BN/KL at radii comparable to the Solar System

2009 ◽  
Vol 5 (H15) ◽  
pp. 750-750 ◽  
Author(s):  
C. Goddi ◽  
L. Greenhill ◽  
E. Humphreys ◽  
L. Matthews ◽  
C. Chandler
Keyword(s):  
Accretion Disks ◽  
Gas Flow ◽  
Dynamical Evolution ◽  
Young Stellar Objects ◽  
High Mass ◽  
Mass Star ◽  
Proper Motions ◽  
Compact Disk ◽  
Stellar Objects ◽  
Circumstellar Gas

Around high-mass Young Stellar Objects (YSOs), outflows are expected to be launched and collimated by accretion disks inside radii of 100 AU. Strong observational constraints on disk-mediated accretion in this context have been scarce, largely owing to difficulties in probing the circumstellar gas at scales 10-100 AU around high-mass YSOs, which are on average distant (>1 Kpc), form in clusters, and ignite quickly whilst still enshrouded in dusty envelopes. Radio Source I in Orion BN/KL is the nearest example of a high-mass YSO, and only one of three YSOs known to power SiO masers. Using VLA and VLBA observations of different SiO maser transitions, the KaLYPSO project (http://www.cfa.harvard.edu/kalypso/) aims to overcome past observational limitations by mapping the structure, 3-D velocity field, and dynamical evolution of the circumstellar gas within 1000 AU from Source I. Based on 19 epochs of VLBA observations of v=1,2 SiO masers over ~2 years, we produced a movie of bulk gas flow tracing the compact disk and the base of the protostellar wind at radii < 100 AU from Source I. In addition, we have used the VLA to map 7mm SiO v=0 emission and track proper motions over 10 years. We identify a narrowly collimated outflow with a mean motion of 18 km/s at radii 100-1000 AU, along a NE-SW axis perpendicular to that of the disk traced by the v=1,2 masers. The VLBA and VLA data exclude alternate models that place outflow from Source I along a NW-SE axis. The analysis of the complete (VLBA and VLA) dataset provides the most detailed evidence to date that high-mass star formation occurs via disk-mediated accretion.

scholarly journals Radio Jets in Young Stellar Objects with the SKA

2015 ◽  
Author(s):  
Guillem Anglada ◽  
Luis Felipe Rodríguez ◽  
Carlos Carrasco-Gonzalez
Keyword(s):  
Young Stellar Objects ◽  
Stellar Objects ◽  
Radio Jets
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