scholarly journals Launching jets from the boundary layer of accretion disks in young stellar objects

2003 ◽  
Vol 406 (2) ◽  
pp. 603-611 ◽  
Author(s):  
N. Soker ◽  
O. Regev
Keyword(s):  
Boundary Layer ◽  
Accretion Disks ◽  
Young Stellar Objects ◽  
Stellar Objects

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 On the Mass Accretion Rates of Herbig Ae/Be Stars. Magnetospheric Accretion or Boundary Layer?

Galaxies ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 39
Author(s):  
Ignacio Mendigutía
Keyword(s):  
Boundary Layer ◽  
Magnetic Fields ◽  
Young Stellar Objects ◽  
Driving Mechanism ◽  
Be Stars ◽  
Stellar Objects ◽  
Star Forming ◽  
T Tauri ◽  
Accretion Rates ◽  
Magnetospheric Accretion

Understanding how young stars gain their masses through disk-to-star accretion is of paramount importance in astrophysics. It affects our knowledge about the early stellar evolution, the disk lifetime and dissipation processes, the way the planets form on the smallest scales, or the connection to macroscopic parameters characterizing star-forming regions on the largest ones, among others. In turn, mass accretion rate estimates depend on the accretion paradigm assumed. For low-mass T Tauri stars with strong magnetic fields there is consensus that magnetospheric accretion (MA) is the driving mechanism, but the transfer of mass in massive young stellar objects with weak or negligible magnetic fields probably occurs directly from the disk to the star through a hot boundary layer (BL). The intermediate-mass Herbig Ae/Be (HAeBe) stars bridge the gap between both previous regimes and are still optically visible during the pre-main sequence phase, thus constituting a unique opportunity to test a possible change of accretion mode from MA to BL. This review deals with our estimates of accretion rates in HAeBes, critically discussing the different accretion paradigms. It shows that although mounting evidence supports that MA may extend to late-type HAes but not to early-type HBes, there is not yet a consensus on the validity of this scenario versus the BL one. Based on MA and BL shock modeling, it is argued that the ultraviolet regime could significantly contribute in the future to discriminating between these competing accretion scenarios.

scholarly journals Analysis of physical processes in eruptive YSOs with near-infrared spectra and multiwavelength light curves

2021 ◽  
Vol 504 (1) ◽  
pp. 830-856
Author(s):  
Zhen Guo (郭震) ◽  
P W Lucas ◽  
C Contreras Peña ◽  
L C Smith ◽  
C Morris ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Infrared Spectra ◽  
Near Infrared ◽  
Total Duration ◽  
Light Curves ◽  
Young Stellar Objects ◽  
Multiple Time ◽  
Dynamic Interactions ◽  
Stellar Objects ◽  
Near Infrared Spectra

ABSTRACT The decade-long Vista Variables in the Via Lactea (VVV) survey has detected numerous highly variable young stellar objects (YSOs). We present a study of 61 highly variable VVV YSOs (ΔKs = 1–5 mag), combining near-infrared spectra from Magellan and ESO Very Large Telescope with VVV and NEOWISE light curves to investigate physical mechanisms behind eruptive events. Most sources are spectroscopically confirmed as eruptive variables (typically Class I YSOs) but variable extinction is also seen. Among them, magnetically controlled accretion, identified by H i recombination emission (usually accompanied by CO emission), is observed in 46 YSOs. Boundary layer accretion, associated with FU Ori-like outbursts identified by CO overtone and H2O absorption, is observed only in longer duration events (≥5 yr total duration). However, even in long duration events, the magnetically controlled accretion mode predominates, with amplitudes similar to the boundary layer mode. Shorter (100–700 d) eruptive events usually have lower amplitudes and these events are generally either periodic accretors or multiple time-scale events, wherein large photometric changes occur on time-scales of weeks and years. We find that the ratio of amplitudes in Ks and W2 can distinguish between variable accretion and variable extinction. Several YSOs are periodic or quasi-periodic variables. We identify examples of periodic accretors and extinction-driven periodicity among them (with periods up to 5 yr) though more data are needed to classify some cases. The data suggest that dynamic interactions with a companion may control the accretion rate in a substantial proportion of eruptive systems, although star–disc interactions should also be considered.

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 Effect of Advected Fields on Accretion Disk Dynamos

1994 ◽  
Vol 142 ◽  
pp. 963-967
Author(s):  
Arun V. Mangalam ◽  
K. Subramanian
Keyword(s):  
Magnetic Fields ◽  
Boundary Conditions ◽  
Accretion Disks ◽  
Binary Systems ◽  
Field Configuration ◽  
Young Stellar Objects ◽  
Subsequent Work ◽  
Stellar Objects ◽  
Seed Field ◽  
Dynamo Equation

AbstractWe present calculations of favored dynamo modes when advection of ambient magnetic fields onto accretion disks is important. These models are relevant for compact binary systems and young stellar objects and can be extended to active galactic nuclei (AGNs). The dynamo equation, including the standard α-effect, is modified to take into account advected magnetic fields. Vacuum boundary conditions are assumed outside the disk and the dynamo number switches sign across the equatorial plane. For the local steady state problem, critical dynamo numbers for various modes are obtained analytically. Our motivation is to investigate whether the dominant dynamo generation of quadrupolar magnetic fields and accretion of dipolar magnetic fields is likely to lead to particle acceleration in the form of jets. The results shown here are for a particular choice of boundary conditions and geometry of the advected field. Besides examining other choices, we shall calculate growth rates for different modes, and the influence of the initial seed field configuration on the evolution of the magnetic fields in subsequent work.Subject headings: acceleration of particles — accretion, accretion disks — binaries: close — galaxies: nuclei — MHD — stars: pre-main-sequence

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