Differential Rotation of the Sun, Helioseismology Data, and Estimation of the Depth of Superconvection Cells

A computational model, based on diffusion, differential rotation, and meridional circulation, has been developed to simulate the transport of magnetic flux on the Sun. Using Kitt Peak magnetograms as input, we have determined a best-fit diffusion constant by comparing the computed and observed fields at later times. Our value of 730 ± 250 km2/s is consistent with Leighton's (1964) estimate of 770–1540 km2/s and is significantly larger than Mosher's (1977) estimate of 200–400 km2/s. This suggests that diffusion may be fast enough to account for the observed polar magnetic field reversal without requiring a significant assist from meridional currents.

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Stellar activity and rotation of the planet host Kepler-17 from long-term space-borne photometry

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833894 ◽

2019 ◽

Vol 626 ◽

pp. A38 ◽

Cited By ~ 4

Author(s):

A. F. Lanza ◽

Y. Netto ◽

A. S. Bonomo ◽

H. Parviainen ◽

A. Valio ◽

...

Keyword(s):

Maximum Entropy ◽

Differential Rotation ◽

Activity Cycle ◽

Magnetic Activity ◽

Model Parameters ◽

The Sun ◽

Level Of Activity ◽

Spot Model ◽

Rotational Evolution ◽

Solar Type

Context. The study of young Sun-like stars is fundamental to understanding the magnetic activity and rotational evolution of the Sun. Space-borne photometry by the Kepler telescope provides unprecedented datasets to investigate these phenomena in Sun-like stars. Aims. We present a new analysis of the entire Kepler photometric time series of the moderately young Sun-like star Kepler-17 accompanied by a transiting hot Jupiter. Methods. We applied a maximum-entropy spot model to the long-cadence out-of-transit photometry of the target to derive maps of the starspot filling factor versus the longitude and the time. These maps are compared to the spots occulted during transits to validate our reconstruction and derive information on the latitudes of the starspots. Results. We find two main active longitudes on the photosphere of Kepler-17, one of which has a lifetime of at least ∼1400 days although with a varying level of activity. The latitudinal differential rotation is of solar type, that is, with the equator rotating faster than the poles. We estimate a minimum relative amplitude ΔΩ/Ω between ∼0.08 ± 0.05 and 0.14 ± 0.05, our determination being affected by the finite lifetime of individual starspots and depending on the adopted spot model parameters. We find marginal evidence of a short-term intermittent activity cycle of ∼48 days and an indication of a longer cycle of 400−600 days characterized by an equatorward migration of the mean latitude of the spots as in the Sun. The rotation of Kepler-17 is likely to be significantly affected by the tides raised by its massive close-by planet. Conclusion. We confirm the reliability of maximum-entropy spot models to map starspots in young active stars and characterize the activity and differential rotation of this young Sun-like planetary host.

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Differential Rotation and Magnetic Activity of the Lower Main Sequence Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100075539 ◽

1980 ◽

Vol 51 ◽

pp. 296-297

Author(s):

G. Belvedere ◽

L. Paterno ◽

M. Stix

Keyword(s):

Spherical Shell ◽

Differential Rotation ◽

Main Sequence ◽

Magnetic Activity ◽

The Sun ◽

Coupling Constant ◽

Main Sequence Stars ◽

Dynamo Theory ◽

Magnetic Cycles ◽

Surface Convection

AbstractWe extend to the lower main sequence stars the analysis of convection interacting with rotation in a compressible spherical shell, already applied to the solar case (Belvedere and Paterno, 1977; Belvedere et al. 1979a). We assume that the coupling constant ε between convection and rotation, does not depend on the spectral type. Therefore we take ε determined from the observed differential rotation of the Sun, and compute differential rotation and magnetic cycles for stars ranging from F5 to MO, namely for those stars which are supposed to possess surface convection zones (Belvedere et al. 1979b, c, d). The results show that the strength of differential rotation decreases from a maximum at F5 down to a minimum at G5 and then increases towards later spectral types. The computations of the magnetic cycles based on the αω-dynamo theory show that dynamo instability decreases from F5 to G5, and then increases towards the later spectral types reaching a maximum at MO. The period of the magnetic cycles increases from a few years at F5 to about 100 years at MO. Also the extension of the surface magnetic activity increases substantially towards the later spectral types. The results are discussed in the framework of Wilson’s (1978) observations.

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Some patterns in the development of centers of solar activity, 1962–66

Symposium - International Astronomical Union ◽

10.1017/s0074180900021318 ◽

1968 ◽

Vol 35 ◽

pp. 56-63 ◽

Cited By ~ 6

Author(s):

Helen W. Dodson ◽

E. Ruth Hedeman

Keyword(s):

Solar Activity ◽

Radio Emission ◽

Differential Rotation ◽

Graphical Representation ◽

Past History ◽

The Sun ◽

Active Centers ◽

Opposite Hemisphere ◽

The Past ◽

History Of

A graphical representation of the 66 solar rotations (Carrington) between January 1, 1962 and December 31, 1966 has been prepared. It includes all centers of activity for which the calcium plage attained an area of at least 1000 millionths of the solar hemisphere and/or intensity 3 (McMath scale). In this study the antecedents, descendents, and neighbors of each region can easily be discerned. The work shows clearly that zones of activity, apparently closely related and much larger than single plages existed for long intervals of time. For example, the significant increases in solar activity in February, May, and October of 1965 occurred in a ‘family’ of calcium plages apparently related through similarities of position and strong radio emission.The members of ‘families’ of centers of activity are found at systematically changing longitudes. For some ‘families’ the change of longitude appears to be primarily a consequence of differential rotation; for others, the pattern of formation of active centers dominates.According to the data for 1962–66 a meaningful study of the development of a center of activity may require consideration not only of the past history of the zone of the Sun in which it occurs but also of the zone approximately 180° away on the opposite hemisphere.

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Large-Scale Internal Magnetic Field of the Sun

Symposium - International Astronomical Union ◽

10.1017/s0074180900044399 ◽

1990 ◽

Vol 138 ◽

pp. 391-394

Author(s):

A.E. Dudorov ◽

V.N. Krivodubskij ◽

A.A. Ruzmaikin ◽

T.V. Ruzmaikina

Keyword(s):

Magnetic Field ◽

Differential Rotation ◽

Large Scale ◽

The Sun ◽

Poloidal Magnetic Field ◽

The Core ◽

Torsional Waves ◽

Formation And Evolution ◽

Field Lines ◽

The Magnetic Field

The behaviour of the magnetic field during the formation and evolution of the Sun is investigated. It is shown that an internal poloidal magnetic field of the order of 104 − 105 G near the core of the Sun may be compatible with differential rotation and with torsional waves, travelling along the magnetic field lines (Dudorov et al., 1989).

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