The differential rotation of G dwarfs

Küker, M.; Rüdiger, G.; Kitchatinov, L. L.

doi:10.1051/0004-6361/201015994

Cited by 99 publications

(127 citation statements)

References 43 publications

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“…As has been shown by Küker & Rüdiger (1999) a likely explanation for the generation of the magnetic field in WTTS can be given in terms of a α 2 -dynamo.…”

Section: The Magnetic Nature Of V410 Taumentioning

confidence: 99%

“…But this shall not keep us from giving qualitative arguments in favor of an α 2 -dynamo here. Following Küker & Rüdiger (1999) for an α 2 -dynamo the field topology exhibit a distinct non-axisymmetric geometry with S1-or A1-type modes (Rüdiger & Hollerbach 2004). The pronounced bipolar magnetic field at the pole (Fig.…”

Section: The Magnetic Nature Of V410 Taumentioning

confidence: 99%

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The magnetic field topology of the weak-lined T Tauri star V410 Tauri

Carroll

Strassmeier

Rice

et al. 2012

A&A

114

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Aims. In a follow-up investigation we present Zeeman-Doppler maps of the weak-lined T Tauri star (WTTS) V410 Tau. As a rapid rotating star and a typical WTTS the stellar surface of V410 Tau is accessible to surface imaging techniques and allows us to detect and reconstruct the major magnetic surface features on this pre-main sequence star. Methods. The polarized signals we are measuring are on the order of 10 −4 to 10 −3 and are hidden well below the noise level of a single observation. A new line profile reconstruction technique based on a singular value decomposition (SVD) allows us to extract the weak polarized line profiles (Stokes V) as well as the intensity profiles (Stokes I). One of the key features of the line profile reconstruction is that the SVD line profiles are amenable to radiative transfer modeling within our Zeeman-Doppler Imaging code iMap. The code also utilizes a new iterative regularization scheme which is independent of any additional surface constraints. To provide more stability a vital part of our inversion strategy is to invert both Stokes I and Stokes V profiles to simultaneously reconstruct the temperature and magnetic field surface distribution of V410 Tau. A new image-shear analysis is also implemented to allow the search for image and line profile distortions induced by a differential rotation of the star. Results. The magnetic field structure we obtain for V410 Tau shows a good spatial correlation with the surface temperature and is dominated by a strong field within the cool polar spot. The Zeeman-Doppler maps exhibit a large-scale organization of both polarities around the polar cap in the form of a twisted bipolar structure. The magnetic field reaches a value of almost 2 kG within the polar region but smaller fields are also present down to lower latitudes. The pronounced non-axisymmetric field structure and the nondetection of a differential rotation for V410 Tau supports the idea of an underlying α 2 -type dynamo, which is predicted for WTTS.

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“…As has been shown by Küker & Rüdiger (1999) a likely explanation for the generation of the magnetic field in WTTS can be given in terms of a α 2 -dynamo.…”

Section: The Magnetic Nature Of V410 Taumentioning

confidence: 99%

Section: The Magnetic Nature Of V410 Taumentioning

confidence: 99%

The magnetic field topology of the weak-lined T Tauri star V410 Tauri

Carroll

Strassmeier

Rice

et al. 2012

A&A

114

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“…Tobias, Weiss & Kirk 1995;Knobloch, Tobias & Weiss 1998;Tobias 2002;Spiegel 2008;Weiss & Thompson 2008), while similar patterns of behaviour also appear for models based on nonlinear partial differential equations (e.g. Tobias 1997;Küker, Arlt & Rüdiger 1999;Pipin 1999;Weiss 2005Weiss , 2010Bushby 2006;Tobias & Weiss 2007a,b).…”

Section: Introductionmentioning

confidence: 99%

Supermodulation of the Sun's magnetic activity: the effects of symmetry changes

Weiss¹,

Tobias²

2015

Mon. Not. R. Astron. Soc.

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In this paper we argue that the solar activity record, as revealed by telescopic observations and proxy data from the abundances of cosmogenic isotopes, is consistent with the action of a deterministic nonlinear chaotic dynamo. In particular we claim that the long timescale 'super-modulation' apparent in the isotopic record can be ascribed to switching of the dynamo between two different modulational patterns. The first (which is currently in operation) involves deep grand minima and occasional changes in symmetry triggered by these minima. The second, which exhibits only weak modulation and no grand minima, arises as a consequence of symmetry breaking. These processes are demonstrated for highly idealized simple models of the nonlinear dynamo equations.

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“…The conventional α−Ω dynamo cannot work in such a situation. Several alternative dynamo concepts have been developed for fully convective stars (e.g., Giampapa et al 1996;Küker & Rüdiger 1999;Dobler et al 2006;Chabrier & Küker 2006;Browning & Basri 2007;Vögler & Schüssler 2007;Pietarila Graham et al 2010). Although the reliability of these theoretical models is not entirely clear, there is good evidence for the simultaneous presence of an α−Ω dynamo and some kind of a small-scale turbulent dynamo in the convection zone of our Sun (e.g., Durney et al 1993;Trujillo Bueno et al 2004).…”

Section: Introductionmentioning

confidence: 99%

X-ray activity and rotation of the young stars in IC 348

Alexander

Preibisch

2012

A&A

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Context. The physical origin of the strong magnetic activity in T Tauri stars and its relation to stellar rotation is not yet wellunderstood. Aims. We investigate the relation between the X-ray activity, rotation, and Rossby number for a sample of young stars in the ≈3 Myr old cluster IC 348. Methods. We use the data of four Chandra observations of IC 348 to derive the X-ray luminosities of the young stars. Basic stellar parameters and rotation rates are collected from the literature. This results in a sample of 82 X-ray detected stars with known rotation periods. We determine the Rossby numbers (i.e. the ratio of rotation period to convective turnover time) of 76 of these stars from stellar structure-and evolution-models for pre-main sequence stars.Results. The young stars in IC 348 show no correlation between X-ray activity and rotation period. For the Rossby numbers, nearly all IC 348 stars are in the saturated regime of the activity-rotation relation defined by main-sequence stars. Searching for possible super-saturation effects, we find a marginal (but statistically in-significant) trend that the stars with the smallest Rossby numbers have slightly lower X-ray activity levels. There are no significant differences in the X-ray activity level for stars of different spectral types and no relation between spectral type and Rossby number is seen. In addition, for stars belonging to different IR-classes, no significant differences are present for the X-ray activity level as well as for their Rossby numbers. We compare the dispersion in the fractional X-ray luminosities of the stars in the saturated rotation regime in IC 348 to that seen in younger and older stellar populations. The scatter seen in the ≈3 Myr old IC 348 [σ log (L X /L bol ) = 0.43] is considerably smaller than for the ≈1 Myr old Orion nebula cluster [σ log(L X /L bol ) = 0.63], but, at the same time, considerably larger than the dispersion seen in the ≈30 Myr old cluster NGC 2547 [σ log(L X /L bol ) = 0.24] and in main-sequence stars. Conclusions. The results of our X-ray analysis of IC 348 show that neither the rotation rates nor the presence/absence of circumstellar disks are of fundamental importance for determining the level of X-ray activity in TTS. Our results suggest that the scatter in the X-ray activity levels for the rapidly rotating members of young clusters decreases with the age of the stellar population. We interpret this as a signature of the changing interior structure of pre-main sequence stars and the consequent changes in the dynamo mechanisms that are responsible for the magnetic field generation.

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The differential rotation of G dwarfs

Cited by 99 publications

References 43 publications

The magnetic field topology of the weak-lined T Tauri star V410 Tauri

The magnetic field topology of the weak-lined T Tauri star V410 Tauri

Supermodulation of the Sun's magnetic activity: the effects of symmetry changes

X-ray activity and rotation of the young stars in IC 348

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