scholarly journals Magnetic fields of weak line T-Tauri stars

2016 ◽  
Vol 12 (S328) ◽  
pp. 101-106
Author(s):  
Colin A. Hill ◽  
Keyword(s):  
Magnetic Fields ◽  
T Tauri Stars ◽  
Doppler Imaging ◽  
Mass Star ◽  
Weak Line ◽  
T Tauri ◽  
Internal Structures ◽  
Low Mass ◽  
And Migration ◽  
Pms Stars

AbstractT-Tauri stars (TTS) are late-type pre-main-sequence (PMS) stars that are gravitationally contracting towards the MS. Those that possess a massive accretion disc are known as classical T-Tauri stars (cTTSs), and those that have exhausted the gas in their inner discs are known as weak-line T-Tauri stars (wTTSs). Magnetic fields largely dictate the angular momentum evolution of TTS and can affect the formation and migration of planets. Thus, characterizing their magnetic fields is critical for testing and developing stellar dynamo models, and trialling scenarios currently invoked to explain low-mass star and planet formation. The MaTYSSE programme (Magnetic Topologies of Young Stars and the Survival of close-in Exoplanets) aims to determine the magnetic topologies of ~30 wTTSs and monitor the long-term topology variability of ~5 cTTSs. We present several wTTSs that have been magnetically mapped thus far (using Zeeman Doppler Imaging), where we find a much wider range of field topologies compared to cTTSs and MS dwarfs with similar internal structures.

scholarly journals The Surface Magnetic Activity of the Weak-Line T Tauri Stars TWA 7 and TWA 25

2021 ◽  
Author(s):  
B A Nicholson ◽  
G Hussain ◽  
J-F Donati ◽  
D Wright ◽  
C P Folsom ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Radial Velocity ◽  
Large Scale ◽  
T Tauri Stars ◽  
Doppler Imaging ◽  
Weak Line ◽  
T Tauri ◽  
Wide Range ◽  
Velocity Variations ◽  
Scale Surface

Abstract We present an analysis of spectropolarimetric observations of the low-mass weak-line T Tauri stars TWA 25 and TWA 7. The large-scale surface magnetic fields have been reconstructed for both stars using the technique of Zeeman Doppler imaging. Our surface maps reveal predominantly toroidal and non-axisymmetric fields for both stars. These maps reinforce the wide range of surface magnetic fields that have been recovered, particularly in pre-main sequence stars that have stopped accreting from the (now depleted) central regions of their discs. We reconstruct the large scale surface brightness distributions for both stars, and use these reconstructions to filter out the activity-induced radial velocity jitter, reducing the RMS of the radial velocity variations from 495 m s −1 to 32 m s −1 for TWA 25, and from 127 m s −1 to 36 m s −1 for TWA 7, ruling out the presence of close-in giant planets for both stars. The TWA 7 radial velocities provide an example of a case where the activity-induced radial velocity variations mimic a Keplerian signal that is uncorrelated with the spectral activity indices. This shows the usefulness of longitudinal magnetic field measurements in identifying activity-induced radial velocity variations.

scholarly journals The Quest for X-Rays from Protostars

1998 ◽  
Vol 188 ◽  
pp. 17-20 ◽  
Author(s):  
Thierry Montmerle
Keyword(s):  
T Tauri Stars ◽  
Mass Star ◽  
X Rays ◽  
Weak Line ◽  
Rapid Progress ◽  
Class Iii ◽  
Molecular Outflows ◽  
T Tauri ◽  
Evolutionary Scheme ◽  
Low Mass

The field of low-mass star formation and early evolution has made rapid progress in recent years, thanks in particular to observations in the IR and mm ranges. The current evolutionary scheme calls for two main stages, themselves divided into two substages (e.g., André & Montmerle 1994): (i) protostars, comprizing the newly discovered so-called “Class 0 sources”, detected mostly or only in the mm range, which are young protostars with estimated ages ~ 104 yrs, and “Class I sources”, visible in the near- to mid-IR, which are evolved protostars with estimated ages ~ 105 yrs; (ii) T Tauri stars, which are visible in the IR but also in the optical, the younger being the “classical” T Tauri stars (called “Class II” in the IR), and the “weak-line” T Tauri stars (“Class III” in the IR), with a large age spread of ~ 106 – 107 yrs. According to current models (e.g., Shu et al. 1987), protostars consist of a forming star surrounded by an extended envelope (up to ~ 10,000 AU in radius); the star forms via an accretion disk inside a cavity ~ several 100 AU in radius. The disk probably plays an important role in generating molecular outflows, running through the envelope. Classical T Tauri stars are only surrounded by a disk, which disappears at the weak-line T Tauri stage.

scholarly journals Magnetic fields of intermediate-mass T Tauri stars

2019 ◽  
Vol 622 ◽  
pp. A72 ◽  
Author(s):  
F. Villebrun ◽  
E. Alecian ◽  
G. Hussain ◽  
J. Bouvier ◽  
C. P. Folsom ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Main Sequence ◽  
Large Population ◽  
T Tauri Stars ◽  
Magnetic Characteristics ◽  
Intermediate Mass ◽  
Surface Magnetic Field ◽  
T Tauri ◽  
Magnetic Stars ◽  
Pms Stars

Context. The origin of the fossil magnetic fields detected in 5 to 10% of intermediate-mass main sequence stars is still highly debated.Aims. We want to bring observational constraints to a large population of intermediate-mass pre-main sequence (PMS) stars in order to test the theory that convective-dynamo fields generated during the PMS phases of stellar evolution can occasionally relax into fossil fields on the main sequence.Methods. Using distance estimations, photometric measurements, and spectropolarimetric data from HARPSpol and ESPaDOnS of 38 intermediate-mass PMS stars, we determined fundamental stellar parameters (Teff,Landvsini) and measured surface magnetic field characteristics (including detection limits for non-detections, and longitudinal fields and basic topologies for positive detections). Using PMS evolutionary models, we determined the mass, radius, and internal structure of these stars. We compared different PMS models to check that our determinations were not model-dependant. We then compared the magnetic characteristics of our sample accounting for their stellar parameters and internal structures.Results. We detect magnetic fields in about half of our sample. About 90% of the magnetic stars have outer convective envelopes larger than ∼25% of the stellar radii, and heavier than ∼2% of the stellar mass. Going to higher mass, we find that the magnetic incidence in intermediate-mass stars drops very quickly, within a timescale on the order of few times 0.1 Myr. Finally, we propose that intermediate-mass T Tauri stars with large convective envelopes, close to the fully convective limit, have complex fields and that their dipole component strengths may decrease as the sizes of their convective envelopes decrease, similar to lower-mass T Tauri stars.

Magnetic fields of T Tauri stars and inner accretion discs

2018 ◽  
Vol 14 (A30) ◽  
pp. 121-121
Author(s):  
Jean-Francois Donati
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Near Infrared ◽  
High Sensitivity ◽  
T Tauri Stars ◽  
Accretion Discs ◽  
High Resolution Spectroscopy ◽  
T Tauri ◽  
Low Mass ◽  
The Impact

AbstractMagnetic fields play a key role in the early life of stars and their planets, as they form from collapsing dense cores that progressively flatten into large-scale accretion discs and eventually settle as young suns orbited by planetary systems. Pre-main-sequence phases, in which central protostars feed from surrounding planet-forming accretion discs, are especially crucial for understanding how worlds like our Solar System are born.Magnetic fields of low-mass T Tauri stars (TTSs) are detected through high-resolution spectroscopy and spectropolarimetry (e.g., Johns Krull 2007), whereas their large-scale topologies can be inferred from time series of Zeeman signatures using tomographic techniques inspired from medical imaging (Donati & Landstreet 2009). Large-scale fields of TTSs are found to depend on the internal structure of the newborn star, allowing quantitative models of how TTSs magnetically interact with their inner accretion discs, and the impact of this interaction on the subsequent stellar evolution (e.g., Romanova et al. 2002, Zanni & Ferreira 2013).With its high sensitivity to magnetic fields, SPIRou, the new near-infrared spectropolarimeter installed in 2018 at CFHT (Donati et al. 2018), should yield new advances in the field, especially for young embedded class-I protostars, thereby bridging the gap with radio observations.

A Lambda3.6 CM Radio Survey of Low-Mass, weak-Line T Tauri Stars in Taurus- Auriga

1996 ◽  
Vol 111 ◽  
pp. 355 ◽  
Author(s):  
Eugene Chiang ◽  
R. B. Phillips ◽  
C. J. Lonsdale
Keyword(s):  
T Tauri Stars ◽  
Weak Line ◽  
T Tauri ◽  
Low Mass ◽  
Radio Survey

scholarly journals T Tauri stars: magnetic fields and planets

2021 ◽  
Vol 2 (1) ◽  
pp. 9-20
Author(s):  
Konstantin Grankin
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Magnetic Coupling ◽  
Short Review ◽  
T Tauri Stars ◽  
Young Stars ◽  
Doppler Imaging ◽  
Hot Jupiters ◽  
T Tauri

In this short review we present the results of a study of the large-scale magnetic topologies of T Tauri stars (TTS). A small spectropolarimetric survey of 8 young stars was carried out within two international projects MaPP (Magnetic Protostars and Planets) and MaTYSSE (Magnetic Topologies of Young Stars and the Survival of massive close-in Exoplanets) between 2009 and 2016. For each of our targets we reconstructed the brightness map and the magnetic field topology using Zeeman–Doppler imaging (ZDI). This review contains a brief description of spectropolarimetricdata, the ZDI method, one example of the reconstruction of brightness and magnetic maps, and the properties of magnetic fields of 8 TTS. Our results suggest that AA Tau and LkCa 15 interact with their disks in the propeller mode when their rotation is actively slowed by the star/disk magnetic coupling. We find that magnetic fields of some TTS are variable on a time scale of a few years and are thus intrinsically nonstationary. We report on the detection of a giant exoplanet around V830 Tau and TAP 26. These two new detections suggest that the type II disk migration is efficient at generating newborn hot Jupiters (hJs) around young TTS. The result of our survey is compared to the global picture of magnetic field properties of twenty TTS in the Hertzsprung–Russell diagram. The comparison shows that WTTS exhibit a wider range of field topologies as compared to CTTS, and that magnetic fields of all TTS (CTTS and WTTS as a whole) are mostly poloidal and axisymmetric when they are mostly convective and cooler than 4300 K. This needs to be confirmed with a larger sample of stars.

scholarly journals The Interaction of T-Tauri Stars with Molecular Clouds

1980 ◽  
Vol 87 ◽  
pp. 165-172 ◽  
Author(s):  
Joseph Silk ◽  
Colin Norman
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
T Tauri Stars ◽  
Mass Star ◽  
Internal Source ◽  
Low Mass Stars ◽  
Dark Cloud ◽  
Nearby Star ◽  
T Tauri ◽  
Low Mass

Winds from T-Tauri stars may provide an important dynamical input into cold molecular clouds. If the frequency of T-Tauri stars exceeds 20 pc-3, wind-driven shells collide and form ram pressure confined clumps. The supersonic clump motions can account for cloud line widths. Clumps collide inelastically, coalescing and eventually becoming Jeans unstable. For characteristic dark cloud temperatures low mass stars form, and we speculate that in this manner clouds can be self-sustaining for 107 − 108 yr. Only when either the gas supply is exhausted or an external trigger stimulates massive star formation (for example, by heating the cloud or enhancing the clump collision rate), will the cloud eventually be disrupted. A natural consequence of this model is that dark cloud lifetimes are identified with the duration of low mass star formation, inferred to exceed 107 yr from studies of nearby star clusters. Other implications include the prediction of the existence of embedded low mass stars in turbulent cloud cores, the presence of an internal source of radiation in dark clouds, and a clumpy structure for cold molecular clouds.

scholarly journals Spectroscopic analysis of accretion/ejection signatures in the Herbig Ae/Be stars HD 261941 and V590 Mon

2020 ◽  
Vol 494 (3) ◽  
pp. 3512-3535 ◽  
Author(s):  
T Moura ◽  
S H P Alencar ◽  
A P Sousa ◽  
E Alecian ◽  
Y Lebreton
Keyword(s):  
Magnetic Fields ◽  
T Tauri Stars ◽  
Be Stars ◽  
Intermediate Mass ◽  
Stellar Cluster ◽  
Circumstellar Material ◽  
T Tauri ◽  
Low Mass ◽  
Circumstellar Environment ◽  
Magnetospheric Accretion

ABSTRACT Herbig Ae/Be (HAeBe) stars are the intermediate-mass analogues of low-mass T Tauri stars. Both groups may present signs of accretion, outflow, and IR excess related to the presence of circumstellar discs. Magnetospheric accretion models are generally used to describe accreting T Tauri stars, which are known to have magnetic fields strong enough to truncate their inner discs and form accretion funnels. Since few HAeBe stars have had magnetic fields detected, they may accrete through a different mechanism. Our goal is to analyse the morphology and variability of emission lines that are formed in the circumstellar environment of HAeBe stars and use them as tools to understand the physics of the accretion/ejection processes in these systems. We analyse high-resolution (R ∼ 47 000) UVES/ESO spectra of two HAeBe stars – HD 261941 (HAe) and V590 Mon (HBe) that are members of the young (∼3 Myr) NGC 2264 stellar cluster and present indications of sufficient circumstellar material for accretion and ejection processes to occur. We determine stellar parameters with synthetic spectra, and also analyse and classify circumstellar lines such as H α, H β, and He i λ5875.7, according to their morphologies. We model the H α mean line profile, using a hybrid Magnetohydrodynamics (MHD) model that includes a stellar magnetosphere and a disc wind, and find signatures of magnetically driven outflow and accretion in HD 261941, while the H α line of V590Mon seems to originate predominantly in a disc wind.

scholarly journals NMA Imaging of Envelopes and Disks around Low Mass Protostars and T Tauri Stars

1997 ◽  
Vol 182 ◽  
pp. 381-390
Author(s):  
Yoshimi Kitamura ◽  
Masao Saito ◽  
Ryohei Kawabe ◽  
Kazuyoshi Sunada
Keyword(s):  
Accretion Disks ◽  
Molecular Clouds ◽  
Protoplanetary Disks ◽  
Hierarchical Structures ◽  
T Tauri Stars ◽  
Mass Star ◽  
Low Mass Stars ◽  
Star Forming ◽  
T Tauri ◽  
Low Mass

We are intensively studying low mass star formation with the radio telescopes at Nobeyama in Japan. Using both the Nobeyama 45 m dish equipped with a 2 × 2 array receiver and the Nobeyama Millimeter Array (NMA), we can cover a very wide spatial range from overall molecular clouds down to compact protoplanetary disks. With the 45 m dish we are investigating hierarchical structures of molecular clouds including star-forming cores. With NMA we are imaging disklike structures (i.e., envelopes, accretion disks, and protoplanetary disks) around protostars and T Tauri stars. Recently, we have completed our survey for dense disklike envelopes around eleven Class 0 & I protostars by NMA. In this paper, we will present our recent results of the disklike envelopes in addition to the previous NMA results of the disks around three T Tauri stars. On the basis of the data, we will discuss the evolution of the disklike structures (dense envelopes → tenuous ones → dispersing ones → accretion disks → protoplanetary ones), and propose a new scenario for the formation of low mass stars.

scholarly journals Magnetic Activity of T Tauri Stars

1992 ◽  
Vol 9 ◽  
pp. 653-654
Author(s):  
T. Montmerle
Keyword(s):  
Solar Activity ◽  
Main Sequence ◽  
Magnetic Activity ◽  
T Tauri Stars ◽  
X Rays ◽  
General Review ◽  
Near Ir ◽  
T Tauri ◽  
Low Mass ◽  
Pms Stars

T Tauri stars (TTS) are low-mass (M ≲ 1M⊙) pre-main sequence (PMS) stars (for a general review, see Bertout 1989). They have long been known to be variable from near-TIV to near-IR wavelengths, on timescales ranging from a few minutes to a few decades. They are observed to flare in many wavenlength rages, from X-rays to the radio, and all the existing evidence is consistent with a very strong magnetic activity, in many ways analogous to solar activity (for a review, see, e.g., Montmerle et al. 1991).

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