Radio Wavelength Observations of Magnetic Fields on Active Dwarf-M, RS CVN and Magnetic Stars,

Context. The origin of the fossil magnetic fields detected in 5 to 10% of intermediate-mass main sequence stars is still highly debated.Aims. We want to bring observational constraints to a large population of intermediate-mass pre-main sequence (PMS) stars in order to test the theory that convective-dynamo fields generated during the PMS phases of stellar evolution can occasionally relax into fossil fields on the main sequence.Methods. Using distance estimations, photometric measurements, and spectropolarimetric data from HARPSpol and ESPaDOnS of 38 intermediate-mass PMS stars, we determined fundamental stellar parameters (Teff,Landvsini) and measured surface magnetic field characteristics (including detection limits for non-detections, and longitudinal fields and basic topologies for positive detections). Using PMS evolutionary models, we determined the mass, radius, and internal structure of these stars. We compared different PMS models to check that our determinations were not model-dependant. We then compared the magnetic characteristics of our sample accounting for their stellar parameters and internal structures.Results. We detect magnetic fields in about half of our sample. About 90% of the magnetic stars have outer convective envelopes larger than ∼25% of the stellar radii, and heavier than ∼2% of the stellar mass. Going to higher mass, we find that the magnetic incidence in intermediate-mass stars drops very quickly, within a timescale on the order of few times 0.1 Myr. Finally, we propose that intermediate-mass T Tauri stars with large convective envelopes, close to the fully convective limit, have complex fields and that their dipole component strengths may decrease as the sizes of their convective envelopes decrease, similar to lower-mass T Tauri stars.

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Binary and multiple magnetic Ap/Bp stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314002403 ◽

2013 ◽

Vol 9 (S302) ◽

pp. 317-319

Author(s):

Denis Rastegaev ◽

Yuri Balega ◽

Vladimir Dyachenko ◽

Alexander Maksimov ◽

Evgenij Malogolovets

Keyword(s):

Magnetic Fields ◽

Proper Motion ◽

Special Astrophysical Observatory ◽

Full Version ◽

Short Period ◽

Magnetic Stars ◽

Total Fraction ◽

Academy Of Sciences ◽

First Time ◽

Prominent Peak

AbstractWe present the results of speckle interferometric observations of 273 magnetic stars most of which are Ap/Bp type. All observations were made at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. We resolved 58 binary and 5 triple stars into individual components. Almost half of these stars were astrometrically resolved for the first time. The fraction of speckle interferometric binaries/multiples in the sample of stars with confirmed magnetic fields is 23%. We expect that the total fraction of binaries/multiples in the sample with account for spectroscopic short-period systems and wide common proper motion pairs can be twice higher. The detected speckle components have a prominent peak in the ρ distribution that corresponds to the closest resolved pairs. Full version of present paper is available in electronic form at http://arxiv.org/abs/1308.3168.

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Pulsation of Rotating Magnetic Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100117117 ◽

1993 ◽

Vol 139 ◽

pp. 134-134

Author(s):

H. Shibahashi ◽

M. Takata

Keyword(s):

Magnetic Field ◽

Fine Structure ◽

Magnetic Fields ◽

Rotation Axis ◽

Dipole Field ◽

Dipole Mode ◽

Magnetic Stars ◽

Ap Stars ◽

The Magnetic Field ◽

Split Frequency

Recently, one of the rapidly oscillating Ap stars, HR 3831, has been found to have an equally split frequency septuplet, though its oscillation seems to be essentially an axisymmetric dipole mode with respect to the magnetic axis which is oblique to the rotation axis (Kurtz et al. 1992; Kurtz 1992). In order to explain this fine structure, we investigate oscillations of obliquely rotating magnetic stars by taking account of the perturbations due to the magnetic fields and the rotation. We suppose that the star is rigidly rotating and that the magnetic field is a dipole field and its axis is oblique to the rotation axis. We treat the effects of the rotation and of the magnetic field as perturbations. In doing so, we suppose that the rotation of the star is slow enough so that the effect of the rotation on oscillations is smaller than that of the magnetic field.

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Planetary Messages in the Doppler Residuals

Symposium - International Astronomical Union ◽

10.1017/s0074180900217415 ◽

2004 ◽

Vol 202 ◽

pp. 20-28

Author(s):

Geoffrey W. Marcy ◽

Debra A. Fischer ◽

R. Paul Butler ◽

Steven S. Vogt

Keyword(s):

Magnetic Fields ◽

Time Scales ◽

Extrasolar Planets ◽

Velocity Fields ◽

Occurrence Rate ◽

High Occurrence ◽

Magnetic Stars ◽

Stellar Magnetic Fields ◽

Host Stars

The Doppler residuals to the Keplerian fits for extrasolar planets reveal important properties of the planets and host stars. Stellar magnetic fields modify the photospheric velocity fields, causing Doppler fluctuations with unknown time scales. This Doppler “jitter”, seen prominently in the magnetic stars Epsilon Eridani and ξ Boo A, compromises the detectability of planets. The Doppler residuals during the transit of HD209458 reveal that the planet orbits in the same direction as the star spins. Moreover, the transit path across the star is nearly parallel to the stellar equator. Most interestingly, the Doppler residuals of known planets often reveal additional coherent variations, probably caused by additional companions. Both 55 Cancri and HD168443 reveal such coherent Doppler residuals. Another five planet–bearing stars observed at Lick show trends in the Doppler residuals indicating the presence of additional companions. Remarkably, about half of the known extrasolar planets reveal such coherent variations. This suggests that stars with planets have a high occurrence rate of harboring more distant companions, planetary or otherwise.

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Theory of The Oblique Pulsator Model For The Rapidly Oscillating Ap Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100018455 ◽

1993 ◽

Vol 137 ◽

pp. 563-565 ◽

Cited By ~ 1

Author(s):

Hiromoto Shibahashi ◽

Masao Takata

Keyword(s):

Magnetic Fields ◽

Rotation Axis ◽

Dipole Mode ◽

Oscillation Pattern ◽

Frequency Pattern ◽

Magnetic Stars ◽

Dipole Oscillation ◽

Ap Stars ◽

The Magnetic Field ◽

Split Frequency

AbstractRecently, one of the rapidly oscillating Ap stars, HR 3831, has been found to have an equally split frequency septuplet, though its oscillation seems to be essentially an axisymmetric dipole mode with respect to the magnetic axis which is oblique to the rotation axis (Kurtz et al. 1992; Kurtz 1992). In order to explain this fine structure, we investigate oscillations of rotating magnetic stars by taking account of the perturbations due to the magnetic fields and the rotation. We show that the magnetic field on axisymmetric dipole modes distorts the dipole oscillation pattern to have axisymmetric octapole components so that the frequency pattern becomes a septuplet rather than a triplet, and that the additional effect of the rotation leads the frequency pattern to be asymmetric. The formula allows us to get information about the magnetic fields, the rotation, and the geometrical configuration of the star from the oscillation data.

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Dissipation of Magnetic Fields in Very Dense Interstellar Clouds and the Magnetic Flux of a Newborn Star

Symposium - International Astronomical Union ◽

10.1017/s007418090009625x ◽

1987 ◽

Vol 115 ◽

pp. 454-455

Author(s):

Toyoharu Umebayashi ◽

Takenori Nakano

Keyword(s):

Magnetic Fields ◽

Magnetic Flux ◽

Magnetic Star ◽

Number Density ◽

Mass Ratio ◽

Interstellar Clouds ◽

Neutral Particles ◽

Surface Field ◽

Magnetic Stars ◽

Dominant Process

The magnetic flux to mass ratio of an interstellar cloud is 104 to 105 times the ratio in a typical magnetic star with a surface field of 1kG, and is at least several hundred times the ratio in most strongly magnetic stars. This excess magnetic flux must be lost in some stage of star formation. The dominant process of magnetic flux loss in ordinary clouds is the drift of charged particles and magnetic fields in the sea of neutral particles (plasma drift, also called ambipolar diffusion). However, even this process is inefficient in a cloud of hydrogen number density nH ≲ 1010 cm−3.

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Erklärung stellarer und planetarer Magnetfelder durch einen turbulenzbedingten Dynamomechanismus

Zeitschrift für Naturforschung A ◽

10.1515/zna-1966-0813 ◽

1966 ◽

Vol 21 (8) ◽

pp. 1285-1296 ◽

Cited By ~ 37

Author(s):

M. Steenbeck ◽

F. Krause

Keyword(s):

Magnetic Field ◽

Angular Velocity ◽

Magnetic Fields ◽

Cross Product ◽

Skin Depth ◽

Electrically Conducting ◽

Magnetic Stars ◽

The Magnetic Field ◽

Component Parallel ◽

Good Agreement

In a foregoing paper 1 the effects of a turbulent motion on magnetic fields were investigated. Especially turbulence was treated under the influence of CORIOLiS-forces and gradients of density and/or turbulence intensity. It was shown that on these conditions the average cross-product of velocity and magnetic field has a non-vanishing component parallel to the average magnetic field. Here we give the consequences of this effect for rotating, electrically conducting spheres.At first a sphere rotating with constant angular velocity is investigated. The quadratic effect provides for dynamo maintainance of the magnetic fields. A field of dipol-type has the weakest condition for maintainance. Applications to the magnetic field of the earth show a good agreement with the conceptions of the physical state of the earth’s core.For a second model differential rotation is included. We have also dynamo maintainance. Since we have to assume that generally the angular velocity is a function decreasing with the distance from the centre of the sphere, the calculations show that we have a preferred self-excited build-up of a quadrupol-type field. This model may be applicable to magnetic stars.Finally we look for dynamo maintainance of alternating fields. We consider the skin-depth to be small compared with the radius of the sphere, then we have plane geometry. The existence of periodical solutions is proved. Applications to the general magnetic field of the sun, which has a period of 22 years, are discussed.

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