Disks and Outflows

AbstractThis paper reviews recent developments in the study of bipolar outflows and their possible collimation by disklike structures. The exciting stars of most bipolar outflows are embedded in dense cores, self-gravitating structures with masses in the range of 1 to 103M⊙. In many cases, these dense cores are flattened, with its major axis aligned perpendicular to the axis of the outflow. These flattened structures, the interstellar toroids, appear to play a role in the large scale (0.1 pc) collimation of the bipolar outflows. However, a considerable number of observations point to the presence of collimation on much smaller scales. In particular, the results of Sargent and collaborators have revealed the existence of circumstellar disks (with radii of ~1000 AU) that are gravitationally bound to their stars. I also review recent models of accretion disks around T Tauri stars have been successful in explaining the general features of the continuum spectra of T Tauri stars from the ultraviolet to the infrared. Some radio results that have not been considered by these models are discussed.

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The Nobeyama Millimeter Array Survey for Protoplanetary Disks Around Protostar Candidates and T Tauri Stars in Taurus

International Astronomical Union Colloquium ◽

10.1017/s0252921100019771 ◽

1994 ◽

Vol 140 ◽

pp. 274-275

Author(s):

Nagayoshi Ohashi ◽

Ryohei Kawabe ◽

Masahiko Hayashi ◽

Masato Ishiguro

Keyword(s):

Protoplanetary Disks ◽

Circumstellar Disks ◽

Stellar Mass ◽

T Tauri Stars ◽

Continuum Emission ◽

Disk Mass ◽

T Tauri ◽

The Continuum

AbstractThe Nobeyama Millimeter Array Survey for protoplanetary disks has been made for 19 protostellar IRAS sources in Taurus; 13 were invisible protostars and 6 were youngest T Tauri stars. We observed the 98 GHz continuum and CS(J=2-1) line emissions simultaneously with spatial resolutions of 2.8”- 8.8” (360 AU-1,200 AU). Unresolved continuum emission was detected from 5 of 6 T Tauri stars and 2 of 13 protostar candidates. The continuum emission arose from compact circumstellar disks. Extended CS emission was detected around 2 T Tauri stars and 11 protostar candidates. There is a remarkable tendency for the detectability for the 98 GHz continuum emission to be small for protostar candidates. This tendency is explained if the mass of protoplanetary disks around protostars is not as large as that around T Tauri stars; the disk mass may increase with the increase of central stellar mass by dynamical accretion in the course of evolution from protostars to T Tauri stars.

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Outflows and particle acceleration in the accretion disks of young stars

EPJ Web of Conferences ◽

10.1051/epjconf/201920109004 ◽

2019 ◽

Vol 201 ◽

pp. 09004

Author(s):

Sergey Khaibrakhmanov ◽

Alexander Dudorov

Keyword(s):

Particle Acceleration ◽

Accretion Disks ◽

High Speed ◽

Large Scale ◽

T Tauri Stars ◽

Radiative Heat Exchange ◽

Current Layer ◽

X Rays ◽

Disk Structure ◽

T Tauri

Magneto-gas-dynamic (MGD) outflows from the accretion disks of T Tauri stars with fossil large-scale magnetic fileld are investigated. We consider two mechanisms of the outflows: rise of the magnetic flux tubes (MFT) formed in the regions of eﬃcient generation of the toroidal magnetic fileld in the disk due to Parker instability, and acceleration of particles in the current layer formed near the boundary between stellar magnetosphere and the accretion disk. Structure of the disk is calculated using our MGD model of the accretion disks. We simulate dynamics of the MFT in frame of slender flux tube approximation taking into account aerodynamic and turbulent drags, and radiative heat exchange with external gas. Particle acceleration in the current layer is investigated on the basis of Sweet-Parker model of magnetic reconnection. Our calculations show that the MFT can accelerate to velocities up to 50 km s-1 causing periodic outflows from the accretion disks. Estimations of the particle acceleration in the current layer are applied to interpret high-speed jets and X-rays observed in T Tauri stars with the accretion disks.

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Dense Cores and Young Stars in Dark Clouds

Symposium - International Astronomical Union ◽

10.1017/s007418090009478x ◽

1987 ◽

Vol 115 ◽

pp. 33-43

Author(s):

Philip C. Myers

Keyword(s):

Circumstellar Disks ◽

T Tauri Stars ◽

Low Mass Stars ◽

Iras Source ◽

Dark Clouds ◽

Dense Cores ◽

T Tauri ◽

Circumstellar Extinction ◽

Molecular Lines ◽

Low Mass

Dark clouds within a few hundred pc of the Sun contain hundreds of condensations with typical size 0.1 pc, density 104 molecules per cubic cm, mass 1 M⊙, and temperature 10 K. These “dense cores” are defined by maps of molecular lines, such as the (J,K)=(1,1) line of ammonia at 1.3 cm wavelength. They are associated with regions of opaque visual obscuration, groups of T Tauri stars, and other cores. They are closely correlated with steep-spectrum, low-luminosity (1-10 L⊙) IRAS sources! of about 60 cores with ammonia maps, half have an IRAS source within one map diameter. Thus cores form low-mass stars, which are probably precursors of T Tauri stars. Simple models indicate that time for a core to wait before collapsing, to collapse and form a star, and to disperse are each of order 105 yr. Cores with stars have broader lines and bigger velocity gradients than cores without stars, suggesting interaction between the star and the core due to gravity and/or outflow. Stars in cores have about 30 mag greater circumstellar extinction, and greater likelihood of CO outflow, than stars near, but not in, cores. Models of the 1-100 μm spectra of stars in cores suggest that inside of ∼100 A.U., the typical star suffers relatively little line-of-sight extinction but is accompanied by a source of significant luminosity at 5-25 μm. Models involving circumstellar disks provide good fits to the observed spectra.

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The role of magnetic fields in pre-main sequence stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314001653 ◽

2013 ◽

Vol 9 (S302) ◽

pp. 25-37 ◽

Cited By ~ 6

Author(s):

Gaitee A. J. Hussain ◽

Evelyne Alecian

Keyword(s):

Magnetic Fields ◽

Large Scale ◽

Main Sequence ◽

Circumstellar Disks ◽

T Tauri Stars ◽

Main Sequence Stars ◽

T Tauri ◽

First Results ◽

Pms Stars

AbstractStrong, kilo-Gauss, magnetic fields are required to explain a range of observational properties in young, accreting pre-main sequence (PMS) systems. We review the techniques used to detect magnetic fields in PMS stars. Key results from a long running campaign aimed at characterising the large scale magnetic fields in accreting T Tauri stars are presented. Maps of surface magnetic flux in these systems can be used to build 3-D models exploring the role of magnetic fields and the efficiency with which magnetic fields can channel accretion from circumstellar disks on to young stars. Long-term variability in T Tauri star magnetic fields strongly point to a dynamo origin of the magnetic fields. Studies are underway to quantify how changes in magnetic fields affect their accretion properties. We also present the first results from a new programme that investigates the evolution of magnetic fields in intermediate mass (1.5–3M⊙) pre-main sequence stars as they evolve from being convective T Tauri stars to fully radiative Herbig AeBe stars.

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The Infancy of Solar-Type Stars and its Relevance for the Origin of Life

International Astronomical Union Colloquium ◽

10.1017/s0252921100014780 ◽

1997 ◽

Vol 161 ◽

pp. 267-282 ◽

Cited By ~ 1

Author(s):

Thierry Montmerle

Keyword(s):

Main Sequence ◽

Solar Nebula ◽

Circumstellar Disks ◽

T Tauri Stars ◽

Necessary Condition ◽

Sequence Evolution ◽

T Tauri ◽

Solar Type ◽

Optical Domain ◽

The Origin Of Life

AbstractFor life to develop, planets are a necessary condition. Likewise, for planets to form, stars must be surrounded by circumstellar disks, at least some time during their pre-main sequence evolution. Much progress has been made recently in the study of young solar-like stars. In the optical domain, these stars are known as «T Tauri stars». A significant number show IR excess, and other phenomena indirectly suggesting the presence of circumstellar disks. The current wisdom is that there is an evolutionary sequence from protostars to T Tauri stars. This sequence is characterized by the initial presence of disks, with lifetimes ~ 1-10 Myr after the intial collapse of a dense envelope having given birth to a star. While they are present, about 30% of the disks have masses larger than the minimum solar nebula. Their disappearance may correspond to the growth of dust grains, followed by planetesimal and planet formation, but this is not yet demonstrated.

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Aperture synthesis CS and 98 GHz continuum observations of protostellar IRAS sources in Taurus

Symposium - International Astronomical Union ◽

10.1017/s0074180900239673 ◽

1991 ◽

Vol 147 ◽

pp. 353-356

Author(s):

N. Ohashi ◽

R. Kawabe ◽

M. Hayashi ◽

M. Ishiguro

Keyword(s):

Molecular Cloud ◽

Total Mass ◽

T Tauri Stars ◽

Continuum Emission ◽

Beam Size ◽

Dust Grains ◽

Dynamical Mass ◽

T Tauri ◽

Cloud Cores ◽

The Continuum

The CS (J = 2 — 1) line and 98 GHz continuum emission have been observed for 11 protostellar IRAS sources in the Taurus molecular cloud with resolutions of 2.6″−8.8″ (360 AU—1200 AU) using the Nobeyama Millimeter Array (NMA). The CS emission is detected only toward embedded sources, while the continuum emission from dust grains is detected only toward visible T Tauri stars except for one embedded source, L1551-IRS5. This suggests that the dust grains around the embedded sources do not centrally concentrate enough to be detected with our sensitivity (∼4 m Jy r.m.s), while dust grains in disks around the T Tauri stars have enough total mass to be detected with the NMA. The molecular cloud cores around the embedded sources are moderately extended and dense enough to be detected in CS, while gas disks around the T Tauri are not detected because the radius of such gas disks may be smaller than 70 (50 K/Tex) AU. These results imply that the total amount of matter within the NMA beam size must increase when the central objects evolve into T Tauri stars from embedded sources, suggesting that the compact and highly dense disks around T Tauri stars are formed by the dynamical mass accretion during the embedded protostar phase.

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Variability of Southern T Tauri Stars (VASTT). III. The Continuum Flux Changes of the TW Hydrae Bright Spot

The Astrophysical Journal ◽

10.1086/343110 ◽

2002 ◽

Vol 580 (1) ◽

pp. 343-357 ◽

Cited By ~ 33

Author(s):

C. Batalha ◽

N. M. Batalha ◽

S. H. P. Alencar ◽

D. F. Lopes ◽

E. S. Duarte

Keyword(s):

T Tauri Stars ◽

Bright Spot ◽

T Tauri ◽

The Continuum

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A mid-infrared interferometric survey of the planet-forming region around young Sun-like stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319001625 ◽

2018 ◽

Vol 14 (S345) ◽

pp. 128-131

Author(s):

József Varga ◽

Péter Ábrahám ◽

Lei Chen ◽

Thorsten Ratzka ◽

K. É. Gabányi ◽

...

Keyword(s):

Spectral Feature ◽

Circumstellar Disks ◽

T Tauri Stars ◽

Band Spectrum ◽

Intermediate Mass ◽

Mid Infrared ◽

Disk Structure ◽

T Tauri ◽

General Difference ◽

Herbig Ae Stars

AbstractWe present our results from a mid-infrared interferometric survey targeted at the planet-forming region in the circumstellar disks around low- and intermediate-mass young stars. Our sample consists of 82 objects, including T Tauri stars, Herbig Ae stars, and young eruptive stars. Our main results are: 1) Disks around T Tauri stars are similar to those around Herbig Ae stars, but are relatively more extended once we account for stellar luminosity. 2) From the distribution of the sizes of the mid-infrared emitting region we find that inner dusty disk holes may be present in roughly half of the sample. 3) Our analysis of the silicate spectral feature reveals that the dust in the inner ~1 au region of disks is generally more processed than that in the outer regions. 4) The dust in the disks of T Tauri stars typically show weaker silicate emission in the N band spectrum, compared to Herbig Ae stars, which may indicate a general difference in the disk structure. Our data products are available at VizieR, and at the following web page: http://konkoly.hu/MIDI_atlas.

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Characterising the surface magnetic fields of T Tauri stars with high-resolution near-infrared spectroscopy

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935695 ◽

2019 ◽

Vol 630 ◽

pp. A99 ◽

Cited By ~ 5

Author(s):

A. Lavail ◽

O. Kochukhov ◽

G. A. J. Hussain

Keyword(s):

Magnetic Field ◽

High Resolution ◽

Magnetic Fields ◽

Large Scale ◽

Near Infrared ◽

Field Measurements ◽

T Tauri Stars ◽

Small Scale ◽

Surface Magnetic Field ◽

T Tauri

Aims. In this paper, we aim to characterise the surface magnetic fields of a sample of eight T Tauri stars from high-resolution near-infrared spectroscopy. Some stars in our sample are known to be magnetic from previous spectroscopic or spectropolarimetric studies. Our goals are firstly to apply Zeeman broadening modelling to T Tauri stars with high-resolution data, secondly to expand the sample of stars with measured surface magnetic field strengths, thirdly to investigate possible rotational or long-term magnetic variability by comparing spectral time series of given targets, and fourthly to compare the magnetic field modulus ⟨B⟩ tracing small-scale magnetic fields to those of large-scale magnetic fields derived by Stokes V Zeeman Doppler Imaging (ZDI) studies. Methods. We modelled the Zeeman broadening of magnetically sensitive spectral lines in the near-infrared K-band from high-resolution spectra by using magnetic spectrum synthesis based on realistic model atmospheres and by using different descriptions of the surface magnetic field. We developped a Bayesian framework that selects the complexity of the magnetic field prescription based on the information contained in the data. Results. We obtain individual magnetic field measurements for each star in our sample using four different models. We find that the Bayesian Model 4 performs best in the range of magnetic fields measured on the sample (from 1.5 kG to 4.4 kG). We do not detect a strong rotational variation of ⟨B⟩ with a mean peak-to-peak variation of 0.3 kG. Our confidence intervals are of the same order of magnitude, which suggests that the Zeeman broadening is produced by a small-scale magnetic field homogeneously distributed over stellar surfaces. A comparison of our results with mean large-scale magnetic field measurements from Stokes V ZDI show different fractions of mean field strength being recovered, from 25–42% for relatively simple poloidal axisymmetric field topologies to 2–11% for more complex fields.

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