Dynamo model with a small number of modes and magnetic activity of T Tauri stars

Sokoloff, D.; Nefedov, S. N.; Ermash, A. A.; Ламзин, С. А.

doi:10.1134/s1063773708110054

Cited by 18 publications

(9 citation statements)

References 23 publications

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“…The critical dynamo number |D cr, s | for a quasi-spherical body is within the wide range between 300 and 5 × 10 3 (cf. Shukurov 1990 andSokoloff et al 2008), depending on the details of the rotation curve and the spatial distribution of the dynamo-governing parameters. For the above estimates, |D s | ≈ 5000.…”

Section: Timescale Of Regular Magnetic Fields In Quasi-spherical Galamentioning

confidence: 99%

Evolution of magnetic fields in galaxies and future observational tests with the Square Kilometre Array

Arshakian

Beck

Krause

et al. 2008

A&A

194

246

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Aims. In the context of models of galaxy formation and evolution, we investigate the cosmological evolution of large-and small-scale magnetic fields inside galaxies. Methods. We use the dynamo theory to derive the timescales of amplification and ordering of magnetic fields in disk and puffy galaxies. Turbulence in protogalactic halos generated by thermal virialization can drive an efficient turbulent dynamo. Results from simulations of hierarchical structure formation cosmology provide a tool to develop an evolutionary model of regular magnetic fields coupled with galaxy formation and evolution. Results. The turbulent (small-scale) dynamo was able to amplify a weak seed magnetic field in halos of protogalaxies to a few μG strength within a few 10 8 yr. This turbulent field served as a seed to the mean-field (large-scale) dynamo. Galaxies similar to the Milky Way formed their disks at z ≈ 10 and regular fields of μG strength and a few kpc coherence length were generated within 2 Gyr (at z ≈ 3), but field-ordering on the coherence scale of the galaxy size required an additional 6 Gyr (at z ≈ 0.5). Giant galaxies formed their disks at z ≈ 10, allowing more efficient dynamo generation of strong regular fields (with kpc coherence length) already at z ≈ 4. However, the age of the Universe is short for fully coherent fields in giant galaxies larger than 15 kpc to have been achieved. Dwarf galaxies should have hosted fully coherent fields at z ≈ 1. After a major merger, the strength of the turbulent field is enhanced by a factor of a few. Conclusions. This evolutionary scenario can be tested by measurements of polarized synchrotron emission and Faraday rotation with the planned Square Kilometre Array (SKA). We predict an anticorrelation between galaxy size and ratio between ordering scale and galaxy size. Weak regular fields (small Faraday rotation) in galaxies at z < ∼ 3 are signatures of major mergers. Undisturbed dwarf galaxies should host fully coherent fields, giving rise to strong Faraday rotation signals. Radio observations may serve as a clock for measuring the time since the last major merger.

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Section: Timescale Of Regular Magnetic Fields In Quasi-spherical Galamentioning

confidence: 99%

Evolution of magnetic fields in galaxies and future observational tests with the Square Kilometre Array

Arshakian

Beck

Krause

et al. 2008

A&A

194

246

View full text Add to dashboard Cite

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“…Additional observations of V410 Tau dating from 1905 to 1987 are available on photographic plates in the archives of the Sternberg Astronomy Institute. Sokoloff et al (2008) have digitized this data and used it to investigate the variability over a longer period of time. This revealed a third decrease in light-curve amplitude between 1963 and 1970, this time in the B band.…”

Section: Introductionmentioning

confidence: 99%

Dynamo processes in the T Tauri star V410 Tau

Skelly

Donati

Bouvier

et al. 2010

Monthly Notices of the Royal Astronomical Society

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We present new brightness and magnetic images of the weak‐line T Tauri star V410 Tau, made by using data from the Narval spectropolarimeter at Télescope Bernard Lyot (TBL). The brightness image shows a large polar spot and significant spot coverage at lower latitudes. The magnetic maps show a field that is predominantly dipolar and non‐axisymmetric with a strong azimuthal component. The field is 50 per cent poloidal and 50 per cent toroidal, and very little differential rotation is apparent from the magnetic images. A photometric monitoring campaign on this star has previously revealed V‐band variability of up to 0.6 mag, but in 2009 the light curve is much flatter. The Doppler image presented here is consistent with this low variability. Calculating the flux predicted by the mapped spot distribution gives a peak‐to‐peak variability of 0.04 mag. The reduction in the amplitude of the light curve, compared with previous observations, appears to be related to a change in the distribution of the spots rather than the number or area. This paper is the first from a Zeeman–Doppler imaging campaign being carried out on V410 Tau between 2009 and 2012 at the TBL. During this time, it is expected that the light curve will return to a high‐amplitude state, allowing us to ascertain whether the photometric changes are accompanied by a change in the magnetic field topology.

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“…A dynamo mechanism, if present, is not necessarily cyclic, as needed by our model. However, recently Sokoloff et al (2008) proposed models of dynamos in low-mass, fully convective stars with a cyclic magnetic field. The photometric variability observed in T Tauri stars (e.g., Mel'Nikov & Grankin 2005;Grankin et al 2007) may be related to a corresponding change in the stellar magnetic field (Armitage 1995).…”

Section: Discussionmentioning

confidence: 99%

The Effect of a Stellar Magnetic Variation on the Jet Velocity

Colle

Gracia

Murphy

2008

Astrophysical Journal

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Stellar jets are normally constituted by chains of knots with some periodicity in their spatial distribution, corresponding to a variability of order of several years in the ejection from the protostar/disk system. A widely accepted theory for the presence of knots is related to the generation of internal working surfaces due to variations in the jet ejection velocity. In this paper we study the effect of variations in the inner disk-wind radius on the jet ejection velocity. We show that a small variation in the inner disk-wind radius produces a variation in the jet velocity large enough to generate the observed knots. We also show that the variation in the inner radius may be related to a variation of the stellar magnetic field.

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Dynamo model with a small number of modes and magnetic activity of T Tauri stars

Cited by 18 publications

References 23 publications

Evolution of magnetic fields in galaxies and future observational tests with the Square Kilometre Array

Evolution of magnetic fields in galaxies and future observational tests with the Square Kilometre Array

Dynamo processes in the T Tauri star V410 Tau

The Effect of a Stellar Magnetic Variation on the Jet Velocity

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