Possible variability of the magnetic field of T Tau

Smirnov, D. A.; Ламзин, С. А.; Fabrika, S.; Chuntonov, G. A.

doi:10.1134/1.1774397

Cited by 24 publications

(35 citation statements)

References 13 publications

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“…Observations of the CTTSs type young stars show that possibly the field may vary on the scales of months or even weeks (Smirnov et al 2004;Donati et al 2008). What the time scales of magnetic field variations in neutron stars and white dwarfs are is less clear.…”

Section: Phase Shift Due To Field Reconstructionmentioning

confidence: 99%

“…The magnetic field of young, low-mass stars may vary rapidly due to the dynamo mechanism. Spectropolarimetric observations of young CTTS stars, show that in some stars, the magnetic field can vary as fast as one week ; see also Smirnov et al 2004). This mechanism is evidently important in young stars, where the magnetic field can vary rapidly; the magnetic field of compact stars varies only slowly (e.g., Ruderman 2005).…”

Section: Introductionmentioning

confidence: 99%

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Accretion onto stars with octupole magnetic fields: Matter flow, hot spots and phase shifts

2012

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Recent measurements of the surface magnetic fields of classical T Tauri stars (CTTSs) and magnetic cataclysmic variables show that their magnetic fields have a complex structure. Investigation of accretion onto such stars requires global three-dimensional (3D) magnetohydrodynamic (MHD) simulations, where the complexity of simulations strongly increases with each higher-order multipole. Previously, we were able to model disc accretion onto stars with magnetic fields described by a superposition of dipole and quadrupole moments. However, in some stars, like CTTS V2129 Oph and BP Tau, the octupolar component is significant and it was necessary to include the next octupolar component. Here, we show results of global 3D MHD simulations of accretion onto stars with superposition of the dipole and octupole fields, where we vary the ratio between components. Simulations show that if octupolar field strongly dominates at the disc-magnetosphere boundary, then matter flows into the ring-like octupolar poles, forming ring-shape spots at the surface of the star above and below equator. The light-curves are complex and may have two peaks per period. In case where the dipole field dominates, matter accretes in two ordered funnel streams towards poles, however the polar spots are meridionally-elongated due to the action of the octupolar component. In the case when the fields are of similar strengths, both, polar and belt-like spots are present. In many cases the light-curves show the evidence of complex fields, excluding the cases of small inclinations angles, where sinusoidal light-curve is observed and 'hides' the information about the field complexity.We also propose new mechanisms of phase shift in stars with complex magnetic fields. We suggest that the phase shifts can be connected with: (1) temporal variation of the star's intrinsic magnetic field and subsequent redistribution of main magnetic poles; (2) variation of the accretion rate, which causes the disc to interact with the magnetic fields associated with different magnetic moments. We use our model to demonstrate these phase shift mechanisms, and we discuss possible applications of these mechanisms to accreting millisecond pulsars and young stars.

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Section: Phase Shift Due To Field Reconstructionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Accretion onto stars with octupole magnetic fields: Matter flow, hot spots and phase shifts

2012

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“…Recent measurements of the width of radiofrequency spectral lines (Bell et al 2000), together with discrepancies between experimental data (Smirnov et al 1984;Smirnov 1985;Wilson & Jäger 1987;Sorochenko 1989;Bell et al 2000) and conventional models (Baranger 1958a-c;Griem et al 1959;Griem 1967Griem , 1974 have stimulated the interest in this type of transitions. In this framework a controversy (see Griem 2005 and works cited therein) in explaining these disagreements without changing the usual frame of Stark broadening theories occur.…”

Section: Introductionmentioning

confidence: 99%

Exact expression of the impact broadening operator for hydrogen Stark broadening

Ma¹,

González

Talin³

et al. 2007

A&A

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Aims. Recent measurements on the Stark broadening of radio recombination lines show values and trends in disagreement with conventional theories. Different attemps to explain those disagreements have not been successfull for any of the employed theoretical models. In particular, the impact model that describes well the physical conditions at which the studied broadenings occur, shows a functional trend upon the principal quantum number of the studied transitions that does not correspond to the experimental observations. Methods. High values of the principal quantum number require computable formulas for the calculation of transition probabilities. Some of those expressions have been published, leading to approximate formulas on the dependence of the line width versus the principal quantum number of the upper level of the transition. Results. In this work an exact expression for the hydrogen Stark width in the frame of impact approximation is given.

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“…All these stars are characterized by He i emission lines which have strong narrow components (NCs) to their line profiles (see Edwards et al 1994or Alencar & Basri 2000 for a discussion of NC and broad component, BC, emission in CTTSs). Smirnov et al (2004) reported detections of circular polarization in the He i 5876Å emission line of T Tau on all 3 nights they observed the star, though with significant variability from one night to the next (field measurements range from +350 G to +1100 G with no uncertainty estimates). T Tau's He i line is dominated by BC emission.…”

Section: Magnetic Fields In Accretion Shocks On Cttssmentioning

confidence: 99%

“…As a result, circular polarization in the BC of the He i 5876Å emission is predicted to be less than in the NC. Therefore, the result of Smirnov et al (2004) detections. Such observations can strongly constrain the formation region of the BC emission.…”

Section: Magnetic Fields In Accretion Shocks On Cttssmentioning

confidence: 99%

Measuring T Tauri star magnetic fields

Johns–Krull

2008

Proc. IAU

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Abstract. Stellar magnetic fields including a strong dipole component are believed to play a critical role in the early evolution of newly formed stars and their circumstellar accretion disks. It is currently believed that the stellar magnetic field truncates the accretion disk several stellar radii above the star. This action forces accreting material to flow along the field lines and accrete onto the star preferentially at high stellar latitudes. It is also thought that the stellar rotation rate becomes locked to the Keplerian velocity near the radius where the disk is truncated. This paper reviews recent efforts to measure the magnetic field properties of low mass pre-main sequence stars, focussing on how the observations compare with the theoretical expectations. A picture is emerging indicating that quite strong fields do indeed cover the majority of the surface on these stars; however, the dipole component of the field appears to be alarmingly small. The current measurements also suggest that given their strong magnetic fields, T Tauri stars are somewhat faint in X-rays relative to what is expected from simple main sequence star scaling laws.

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Possible variability of the magnetic field of T Tau

Cited by 24 publications

References 13 publications

Accretion onto stars with octupole magnetic fields: Matter flow, hot spots and phase shifts

Accretion onto stars with octupole magnetic fields: Matter flow, hot spots and phase shifts

Exact expression of the impact broadening operator for hydrogen Stark broadening

Measuring T Tauri star magnetic fields

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