摘要:

AbstractSome questions concerning the formation of mean‐field theories are analyzed by a consideration of simple nonlinear recursions. The results suggest that a general closure scheme does not exist, rather there is a great variety of closures, each of the valid in only a certain interval of the characteristic parameter.Furthermore, questions connected with the appearance of random behaviour in these deterministic systems and the modelling of random reversals are discusse

ISSN:0004-6337    

DOI:10.1002/asna.2113050602

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

摘要:

AbstractThe mean‐field dynamo models developed on the basis of mean‐field magnetohydrodynamics reflect some essential features of the magnetic phenomena accompanying the Earth, the Sun and other cosmical bodies. The magnetic fields of those objects may be understood as superpositions of modes which are obtained if the fields are subjected to Fourier decomposition with respect to the longitudinal coordinate and each Fourier component is split into two parts which are either symmetric or antisymmetric with respect to the equatorial plane. The mean‐field models investigated so far provide no satisfactory explanation for the distinct multimodal structure of the observed fields. Within the framework of the traditional mean‐field concept, and with reasonable assumptions, possibilities of couplings of modes occur only due the back‐reaction of the magnetic field on the motions. These possibilities are discussed, and results of relevant numerical experiments are presented. It is open to question whether couplings of this kind are able to explain the coexistence of modes of the observed fields. A modified mean‐field concept is proposed which implies couplings of modes even without any back‐reaction. Contrary to the couplings due to back‐reaction these couplings imply that, in general, axisymmetric modes are accompanied by non‐

ISSN:0004-6337    

DOI:10.1002/asna.2113050603

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

ISSN:0004-6337    

DOI:10.1002/asna.2113050604

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

摘要:

AbstractAn attempt has been made to examine the role of the secondary α‐effect in the nearly symmetric dynamo. The tensor form of the effect has been found and it is concluded that this effect only plays a role under special assumption of the disturbance velocity field. The secondary alfa effect can amplify the generation of the azimuthal field from the poloidal field in the α2‐dynamo rather than in the αω

ISSN:0004-6337    

DOI:10.1002/asna.2113050605

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

摘要:

AbstractThe principal observational facts on the early‐type magnetic stars are summarized, and interpreted in terms of the oblique rotator model. In the theoretical discussion of the interaction between a large‐scale magnetic field and the star's thermal, gravitational and rotation fields, emphasis is laid on effects that are relevant to both fossil and dynamo theories of the origin of the magnetic fi

ISSN:0004-6337    

DOI:10.1002/asna.2113050606

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

摘要:

AbstractA review of selected photometric and spectrophotometric properties of magnetic stars is given. It is shown that unreddened B–V of magnetic stars around B9 type can be transformed to logTeusing the calibration for normal stars and no systematic errors are introduced. Mechanisms of light variability are discussed. It is concluded that different mechanisms must be operating in different stars.Recently obtained photometric observations of short‐period variability by KURTZand Hβ variability by MADEJet al. are discussed. An information about internal structure and the atmospheric structure of these stars can be derived from these observat

ISSN:0004-6337    

DOI:10.1002/asna.2113050607

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

摘要:

AbstractThe radial velocity of the binary star β CrB was reinvestigated to look for the hypothetical third body, suggested by NEUBAUERSresults. Under the assumption that a systematic difference of 1.4 km/sec between NEUBAUERSresults from 1931–43 and ours from 1971–83 is of instrumental origin, the radial velocities of both epochs can be well represented with the same orbital elements: thus the probability for the existence of a third component in the system is reduced. The eccentricity and the angle of periastron passage of the visual orbit, derived from published speckle interferometric measurements, agree very well with the corresponding elements of the spectroscopic orbit. For the masses of the components those of giant resp. subgiant stars of type A8 and F5 are found. The geometry of the binary β CrB with a magnetic star as the primary component is demonst

ISSN:0004-6337    

DOI:10.1002/asna.2113050608

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

ISSN:0004-6337    

DOI:10.1002/asna.2113050609

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

摘要:

AbstractThe intention of this paper is a summary of long‐time phenomena of magnetic stars which we obtained at the Potsdam Observatory. The considered magnetic stars are γ Equ, HD 9996, 53 Cam, 52, Her, andvCep. Many results have been published already; here, they are compiled and completed by new detai

ISSN:0004-6337    

DOI:10.1002/asna.2113050610

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY

摘要:

AbstractLong‐time observations give evidence of secular variations of the effective magnetic fields for some Ap stars. These secular variations may be interpreted by a precessional motion of the star. The precession of the rotationally flattened star is assumed to be caused either by the orbital motion of a satellite where the plane of the orbit is inclined to the axis of rotation of the star or by rotation of the inner and outer layers of the star around differently inclined axe

ISSN:0004-6337    

DOI:10.1002/asna.2113050611

出版商:WILEY‐VCH Verlag    

年代:1984

数据来源: WILEY