Magnetospheric Accretion in T Tauri Stars

Abstract Classical T Tauri stars with ages of less than 10 Myr possess accretion discs. Magnetohydrodynamic processes at the boundary between the disc and the stellar magnetosphere control the accretion and ejections gas flows. We carried out a long series of simultaneous spectroscopic and photometric observations of the classical T Tauri stars, RY Tauri and SU Aurigae, with the aim to quantify the accretion and outflow dynamics at time-scales from days to years. It is shown that dust in the disc wind is the main source of photometric variability of these stars. In RY Tau, we observed a new effect: during events of enhanced outflow, the circumstellar extinction becomes lower. The characteristic time of changes in outflow velocity and stellar brightness indicates that the obscuring dust is near the star. The outflow activity in both stars is changing on a time-scale of years. Periods of quiescence in the variability of the Hα profile were observed during the 2015–2016 period in RY Tau and during the 2016–2017 period in SU Aur. We interpret these findings in the framework of the magnetospheric accretion model, and we discuss how the global stellar magnetic field can influence the long-term variations of the outflow activity.

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The surface magnetic fields of T Tauri stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309031093 ◽

2008 ◽

Vol 4 (S259) ◽

pp. 447-448

Author(s):

Gaitee A. J. Hussain ◽

Andrew Collier Cameron ◽

Moira Jardine ◽

Jean-Francois Donati

Keyword(s):

Magnetic Field ◽

Main Sequence ◽

T Tauri Stars ◽

Magnetic Field Generation ◽

Surface Magnetic Field ◽

Field Patterns ◽

T Tauri ◽

Show Evidence ◽

Generation Mechanisms ◽

Magnetospheric Accretion

AbstractWe present surface magnetic field maps of the two accreting T Tauri stars, CV Cha and CR Cha. Our magnetic field maps show evidence for strong, complex multi-polar fields similar to those obtained on young rapidly rotating main sequence stars. Both CV Cha and CR Cha show magnetic field patterns that are more complex than those recovered for the lower mass, fully convective T Tauri star, BP Tau.By comparing our maps with previously published maps of classical T Tauri stars, we infer that magnetic field patterns on T Tauris, and their underlying magnetic field generation mechanisms evolve quickly as they develop radiative cores. This may have implications for the efficiency with which T Tauri stars can effectively lock onto their surrounding disks under the magnetospheric accretion model scenario. This, in turn, has implications for the angular momentum evolution of T Tauri stars as they evolve towards the main sequence.

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Time variable funnel flows

Proceedings of the International Astronomical Union ◽

10.1017/s174392130700943x ◽

2007 ◽

Vol 3 (S243) ◽

pp. 71-82 ◽

Cited By ~ 2

Author(s):

Silvia H. P. Alencar

Keyword(s):

Field Configuration ◽

Time Variable ◽

T Tauri Stars ◽

Magnetic Field Configuration ◽

Accretion Process ◽

T Tauri ◽

Model Predictions ◽

The Magnetic Field ◽

Disk Region ◽

Magnetospheric Accretion

AbstractMagnetospheric accretion models are the current consensus to explain the main observed characteristics of classical T Tauri stars. In recent years the concept of a static magnetosphere has been challenged by synoptic studies of classical T Tauri stars that show strong evidence for the accretion process to be dynamic on several timescales and governed by changes in the magnetic field configuration. At the same time numerical simulation results predict evolving funnel flows due to the interaction between the stellar magnetosphere and the inner disk region. In this contribution we will focus on the main recent observational evidences for time variable funnel flows and compare them with model predictions.

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Modeling the Hαline emission around classical T Tauri stars using magnetospheric accretion and disk wind models

Astronomy and Astrophysics ◽

10.1051/0004-6361/201014490 ◽

2010 ◽

Vol 522 ◽

pp. A104 ◽

Cited By ~ 42

Author(s):

G. H. R. A. Lima ◽

S. H. P. Alencar ◽

N. Calvet ◽

L. Hartmann ◽

J. Muzerolle

Keyword(s):

T Tauri Stars ◽

Disk Wind ◽

T Tauri ◽

Magnetospheric Accretion

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Optical photometric variable stars towards Cygnus OB7

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1385 ◽

2019 ◽

Vol 487 (2) ◽

pp. 1765-1776 ◽

Cited By ~ 2

Author(s):

Somnath Dutta ◽

Soumen Mondal ◽

Santosh Joshi ◽

Ramkrishna Das

Keyword(s):

Variable Stars ◽

T Tauri Stars ◽

Light Curves ◽

Main Sequence Stars ◽

Star Forming ◽

Rotation Rates ◽

T Tauri ◽

Photometric Observations ◽

Sky Survey ◽

Magnitude Diagram

ABSTRACT We present optical I-band light curves of the stars towards a star-forming region Cygnus OB7 from 17-night photometric observations. The light curves are generated from a total of 381 image frames with very good photometric precision. From the light curves of 1900 stars and their periodogram analyses, we detect 31 candidate variables including five previously identified. 14 out of 31 objects are periodic and exhibit the rotation rates in the range of 0.15–11.60 d. We characterize those candidate variables using optical/infrared colour–colour diagram and colour–magnitude diagram (CMD). From spectral indices of the candidate variables, it turns out that four are probably Classical T-Tauri stars (CTTSs), rest remain unclassified from present data, they are possibly field stars or discless pre-main-sequence stars towards the region. Based on their location on the various CMDs, the ages of two T Tauri Stars were estimated to be ∼5 Myr. The light curves indicate at least five of the periodic variables are eclipsing systems. The spatial distribution of young variable candidates on Planck 857 GHz (350 $\mu$m) and 2MASS (Two Micron All Sky Survey) Ks images suggest that at least two of the CTTSs are part of the active star-forming cloud Lynds 1003.

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Observations of magnetic fields in Herbig Ae/Be stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319003764 ◽

2018 ◽

Vol 14 (A30) ◽

pp. 123-123

Author(s):

Markus Schöller ◽

Swetlana Hubrig

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

T Tauri Stars ◽

Be Stars ◽

T Tauri ◽

Weak Magnetic Fields ◽

Order Of Magnitude ◽

Field Geometry ◽

Herbig Ae Stars ◽

Magnetospheric Accretion

AbstractModels of magnetically driven accretion reproduce many observational properties of T Tauri stars. For the more massive Herbig Ae/Be stars, the corresponding picture has been questioned lately, in part driven by the fact that their magnetic fields are typically one order of magnitude weaker. Indeed, the search for magnetic fields in Herbig Ae/Be stars has been quite time consuming, with a detection rate of about 10% (e.g. Alecian et al. 2008), also limited by the current potential to detect weak magnetic fields. Over the last two decades, magnetic fields were found in about twenty objects (Hubrig et al. 2015) and for only two Herbig Ae/Be stars was the magnetic field geometry constrained. Ababakr, Oudmaijer & Vink (2017) studied magnetospheric accretion in 56 Herbig Ae/Be stars and found that the behavior of Herbig Ae stars is similar to T Tauri stars, while Herbig Be stars earlier than B7/B8 are clearly different. The origin of the magnetic fields in Herbig Ae/Be stars is still under debate. Potential scenarios include the concentration of the interstellar magnetic field under magnetic flux conservation, pre-main-sequence dynamos during convective phases, mergers, or common envelope developments. The next step in this line of research will be a dedicated observing campaign to monitor about two dozen HAeBes over their rotation cycle.

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The Unusual Photometric Variability of the PMS Star GM Cep

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2015.11 ◽

2015 ◽

Vol 32 ◽

Cited By ~ 5

Author(s):

E. H. Semkov ◽

S. I. Ibryamov ◽

S. P. Peneva ◽

T. R. Milanov ◽

K. A. Stoyanov ◽

...

Keyword(s):

Open Cluster ◽

High Amplitude ◽

Outer Radius ◽

T Tauri Stars ◽

Photometric Data ◽

Spectral Studies ◽

Photometric Variability ◽

T Tauri ◽

Young Open Cluster ◽

Photometric Monitoring

AbstractResults from UBVRI photometric observations of the pre-main sequence star GM Cep obtained in the period 2011 April–2014 August are reported in the paper. Presented data are a continuation of our photometric monitoring of the star started in 2008. GM Cep is located in the field of the young open cluster Trumpler 37 and over the past years it has been an object of intense photometric and spectral studies. The star shows a strong photometric variability interpreted as a possible outburst from EXor type in previous studies. Our photometric data for a period of over six years show a large amplitude variability (ΔV ~ 2.3 mag) and several deep minimums in brightness are observed. The analysis of the collected multicolour photometric data show the typical of UX Ori variables a colour reversal during the minimums in brightness. The observed decreases in brightness have a different shape, and evidences of periodicity are not detected. At the same time, high amplitude rapid variations in brightness typical for the classical T Tauri stars also present on the light curve of GM Cep. The spectrum of GM Cep shows the typical of classical T Tauri stars wide Hα emission line and absorption lines of some metals. We calculate the outer radius of the Hα emitting region as 10.4 ± 0.5 R⊙ and the accretion rate as 1.8 × 10− 7 M⊙ yr− 1.

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