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Rapid Rotation (rapid + rotation)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Rapid rotation, active nests of convection and global-scale flows in solar-likestars

ASTRONOMISCHE NACHRICHTEN, Issue 10 2007
B.P. Brown
Abstract In the solar convection zone, rotation couples with intensely turbulent convection to build global-scale flows of differential rotation and meridional circulation. Our sun must have rotated more rapidly in its past, as is suggested by observations of many rapidly rotating young solar-type stars. Here we explore the effects of more rapid rotation on the patterns of convection in such stars and the global-scale flows which are self-consistently established. The convection in these systems is richly time dependent and in our most rapidly rotating suns a striking pattern of spatially localized convection emerges. Convection near the equator in these systems is dominated by one or two patches of locally enhanced convection, with nearly quiescent streaming flow in between at the highest rotation rates. These active nests of convection maintain a strong differential rotation despite their small size. The structure of differential rotation is similar in all of our more rapidly rotating suns, with fast equators and slower poles. We find that the total shear in differential rotation, as measured by latitudinal angular velocity contrast, ,,, increases with more rapid rotation while the relative shear, ,,/,, decreases. In contrast, at more rapid rotation the meridional circulations decrease in both energy and peak velocities and break into multiple cells of circulation in both radius and latitude. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Rotational velocities of the giants in symbiotic stars , III.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
Evidence of fast rotation in S-type symbiotics
ABSTRACT We have measured the projected rotational velocities (v sin i) in a number of symbiotic stars and M giants using high-resolution spectroscopic observations. On the basis of our measurements and data from the literature, we compare the rotation of mass donors in symbiotics with v sin i of field giants and find that: (i) the K giants in S-type symbiotics rotate at v sin i > 4.5 km s,1, which is 2,4 times faster than the field K giants; (ii) the M giants in S-type symbiotics rotate on average 1.5 times faster than the field M giants. Statistical tests show that these differences are highly significant , p-value <10,3 in the spectral-type bins K2III-K5III, M0III-M6III and M2III-M5III and (iii) our new observations of D'-type symbiotics also confirm that they are fast rotators. As a result of the rapid rotation, the cool giants in symbiotics should have 3,30 times larger mass-loss rates. Our results suggest also that bipolar ejections in symbiotics seem to happen in objects where the mass donors rotate faster than the orbital period. All spectra used in our series of papers can be obtained upon request from the authors. [source]

Convective dynamos in spherical wedge geometry

ASTRONOMISCHE NACHRICHTEN, Issue 1 2010
P.J. Käpylä
Abstract Self-consistent convective dynamo simulations in wedge-shaped spherical shells are presented. Differential rotation is generated by the interaction of convection with rotation. Equatorward acceleration and dynamo action are obtained only for sufficiently rapid rotation. The angular velocity tends to be constant along cylinders. Oscillatory large-scale fields are found to migrate in the poleward direction. Comparison with earlier simulations in full spherical shells and Cartesian domains is made (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Rapid rotation, active nests of convection and global-scale flows in solar-likestars

ASTRONOMISCHE NACHRICHTEN, Issue 10 2007
B.P. Brown
Abstract In the solar convection zone, rotation couples with intensely turbulent convection to build global-scale flows of differential rotation and meridional circulation. Our sun must have rotated more rapidly in its past, as is suggested by observations of many rapidly rotating young solar-type stars. Here we explore the effects of more rapid rotation on the patterns of convection in such stars and the global-scale flows which are self-consistently established. The convection in these systems is richly time dependent and in our most rapidly rotating suns a striking pattern of spatially localized convection emerges. Convection near the equator in these systems is dominated by one or two patches of locally enhanced convection, with nearly quiescent streaming flow in between at the highest rotation rates. These active nests of convection maintain a strong differential rotation despite their small size. The structure of differential rotation is similar in all of our more rapidly rotating suns, with fast equators and slower poles. We find that the total shear in differential rotation, as measured by latitudinal angular velocity contrast, ,,, increases with more rapid rotation while the relative shear, ,,/,, decreases. In contrast, at more rapid rotation the meridional circulations decrease in both energy and peak velocities and break into multiple cells of circulation in both radius and latitude. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

SiO Maser Sources within 30 pc of the Galactic Center

ASTRONOMISCHE NACHRICHTEN, Issue S1 2003
Shuji Deguchi
Abstract Using the Nobeyama 45-m radio telescope, we have observed 314 large amplitude variables within 30 pc of the Galactic center in SiO maser lines. Resulting detections give the radial velocities of 174 stars; light-variation periods have been known for all of these stars. The SiO detection rate increases sharply with the period and it is about twice of the OH maser detection rate. The radial-velocity data show slow and rapid rotations of the outer and inner circumnuclear-disk stars, respectively. Five high-velocity stars were found only at the negative-longitude side of the Galactic center. Estimation of the ages of high velocity stars suggests that these stars must be be accelerated to high velocities within 108 years. [source]