| 1. |
- Kochukhov, Oleg
(författare)
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Surface mapping of magnetic hot stars : Theories versus observations
- 2018
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Ingår i: CONTRIBUTIONS OF THE ASTRONOMICAL OBSERVATORY SKALNATE PLESO. - : SLOVAK ACADEMY SCIENCES ASTRONOMICAL INST. - 1335-1842. ; 48:1, s. 58-65
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Tidskriftsartikel (refereegranskat)abstract
- This review summarises results of recent magnetic and chemical abundance surface mapping studies of early-type stars. We discuss main trends uncovered by observational investigations and consider reliability of spectropolarimetric inversion techniques used to infer these results. A critical assessment of theoretical attempts to interpret empirical magnetic and chemical maps in the framework of, respectively, the fossil field and atomic diffusion theories is also presented. This confrontation of theory and observations demonstrates that 3D MHD models of fossil field relaxation are successful in matching the observed range of surface magnetic field geometries. At the same time, even the most recent time-dependent atomic diffusion calculations fail to reproduce diverse horizontal abundance distributions found in real magnetic hot stars.
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| 2. |
- Krticka, J., et al.
(författare)
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The nature of light variations in magnetic hot stars
- 2018
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Ingår i: CONTRIBUTIONS OF THE ASTRONOMICAL OBSERVATORY SKALNATE PLESO. - : SLOVAK ACADEMY SCIENCES ASTRONOMICAL INST. - 1335-1842. ; 48:1, s. 170-174
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic stars show several types of light variability which is modulated by the stellar rotation. In chemically peculiar stars, the redistribution of the flux in the surface regions with peculiar chemical composition leads to the light variability with a typical amplitude of the order of hundredths of magnitude. The most efficient processes that cause the flux redistribution are bound-bound (line) transitions of iron and bound-free (ionization) transitions of silicon. This type of light variability typically leads to a complex dependence of the amplitude on the wavelength and shows antiphase light curves in the far ultraviolet and visual regions. In hot magnetic stars, the modulation of the stellar wind by the magnetic field and the wind blanketing cause the light variability with a typical amplitude of the order of millimagnitudes. We predict the light variations in selected magnetic hot stars and compare the simulated light curves with light variations derived from observations.
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| 3. |
- Mikulasek, Z., et al.
(författare)
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Differential rotation in magnetic chemically peculiar stars
- 2018
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Ingår i: CONTRIBUTIONS OF THE ASTRONOMICAL OBSERVATORY SKALNATE PLESO. - : SLOVAK ACADEMY SCIENCES ASTRONOMICAL INST. - 1335-1842 .- 1336-0337. ; 48:1, s. 203-207
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic chemically peculiar (mCP) stars constitute about 10% of upper-main-sequence stars and are characterized by strong magnetic fields and abnormal photospheric abundances of some chemical elements. Most of them exhibit strictly periodic light, magnetic, radio, and spectral variations that can be fully explained by a rigidly rotating main-sequence star with persistent surface structures and a stable global magnetic field. Long-term observations of the phase curves of these variations enable us to investigate possible surface differential rotation with unprecedented accuracy and reliability. The analysis of the phase curves in the best-observed mCP stars indicates that the location and the contrast of photometric and spectroscopic spots as well as the geometry of the magnetic field remain constant for at least many decades. The strict periodicity of mCP variables supports the concept that the outer layers of upper-main-sequence stars do not rotate differentially. However, there is a small, inhomogeneous group consisting of a few mCP stars whose rotation periods vary on timescales of decades. The period oscillations may reflect real changes in the angular velocity of outer layers of the stars which are anchored by their global magnetic fields. In CU Vir, V901 On, and perhaps BS Cir, the rotational period variation indicates the presence of vertical differential rotation; however, its exact nature has remained elusive until now. The incidence of mCP stars with variable rotational periods is currently investigated using a sample of fifty newly identified Kepler mCP stars.
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| 4. |
- Shultz, Matthew, et al.
(författare)
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HD 156324 : A Tidally Locked Magnetic SB3 With an Orbitally Disrupted Centrifugal Magnetosphere
- 2018
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Ingår i: CONTRIBUTIONS OF THE ASTRONOMICAL OBSERVATORY SKALNATE PLESO. - : SLOVAK ACADEMY SCIENCES ASTRONOMICAL INST. - 1335-1842. ; 48:1, s. 298-299
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Tidskriftsartikel (refereegranskat)abstract
- Period analysis of radial velocity, equivalent width, and magnetic measurements of the SB3 system HD 156324 yield identical results in all cases, indicating the system is tidally locked with orbital and rotational periods of 1.58 d. Its H alpha emission profile exhibits marked morphological departures from the usual pattern observed amongst magnetic B-type stars, which can plausibly be ascribed to tidal disruption of the gravitocentrifugal potential.
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| 5. |
- Shultz, Matthew, et al.
(författare)
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Rotation, Emission, & Evolution of the Magnetic Early B-type Stars
- 2018
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Ingår i: CONTRIBUTIONS OF THE ASTRONOMICAL OBSERVATORY SKALNATE PLESO. - : SLOVAK ACADEMY SCIENCES ASTRONOMICAL INST. - 1335-1842. ; 48:1, s. 175-179
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Tidskriftsartikel (refereegranskat)abstract
- We report the results of the first population study of 51 magnetic early B-type stars, based upon a large database of high-resolution spectropolarimetry assembled by the MiMeS and BinaMIcS collaborations. Utilizing these data, rotational periods were determined for all but 5 of the sample stars. This enabled us to determine dipole oblique rotator model parameters, rotational parameters, and magnetospheric parameters. We find that the ratio of the Alfven radius to the Kepler corotation radius is highly predictive of whether or not a star displays Ha emission from a Centrifugal Magnetosphere (CM), as expected from theoretical considerations. We also find that CM host stars are systematically younger than the general population, as expected given that CM emission requires rapid rotation and a strong magnetic field, and a strong magnetic field will lead to rapid magnetic braking. We conclude that emission-line magnetic early B-type stars are, almost without exception, strongly magnetized, rapidly rotating, and young.
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| 6. |
- Silvester, James
(författare)
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Modelling complex magnetic fields in stars with radiative envelopes
- 2018
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Ingår i: CONTRIBUTIONS OF THE ASTRONOMICAL OBSERVATORY SKALNATE PLESO. - : SLOVAK ACADEMY SCIENCES ASTRONOMICAL INST. - 1335-1842. ; 48:1, s. 116-123
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic chemically peculiar A and B type stars (Ap/Bp) exhibit strong globally organised magnetic fields, this is combined with strong chemical abundance non-uniformities within the atmosphere. The presence of the magnetic field influences energy and mass transport within the atmosphere of a star, this is thought to cause these observed chemical non-uniformities. These stars offer the ideal laboratory for understanding the interplay between magnetic field structure, atmospheric transport processes and other stellar parameters. With the recent increase in the availability of spectropolarimetric data and by using magnetic Doppler imaging (MDI) techniques, the number of detailed maps of the magnetic structure of Ap/Bp stars is growing. It is now possible to begin to investigate correlations between the magnetic field structure, chemical abundance structures in the photospheres of Ap/Bp stars and other stellar parameters, the first steps in understanding the evolution of such magnetic fields.
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| 7. |
- Vlemmings, Wouter, 1974
(författare)
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Magnetic fields around evolved stars
- 2018
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Ingår i: Contributions of the Astronomical Observatory Skalnate Pleso. - 1335-1842 .- 1336-0337. ; 48:1, s. 187-193
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Tidskriftsartikel (refereegranskat)abstract
- There has long been evidence of magnetic fields in the extended envelopes of asymptotic giant branch (AGB) and red supergiant (RSG) stars. These stars are important contributors to the enrichment of the interstellar medium by dust and heavy elements. Magnetic fields might play a role in the mass loss process responsible. Additionally, magnetic fields, typically in combination with binary companions, have often be suggested to be involved in shaping strongly a-spherical planetary nebulae (PNe). New telescopes and instruments are increasing our knowledge about magnetic fields around these evolved, mass losing, stars and their descendants.
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