The accelerating rotation of the magnetic He-weak star HD 142990

Shultz, Matthew; Rivinius, Thomas; Das, B.N.; Wade, G. A.; Chandra, Poonam

doi:10.1093/mnras/stz1129

Cited by 27 publications

(23 citation statements)

References 60 publications

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“…For other B type stars of CU Vir, HD 37776, HD 142990 (Pyper et al 1998;Mikulášek et al 2008;Mikulášek 2016;Shultz et al 2019), and, more recently, 13 And and V913 Sco (Pyper & Adelman 2020) -decreasing rotational periods have even been found, indicating that these stars accelerate their surface rotation. Obviously, this is inconsistent with the prediction of the magnetic braking theory.…”

Section: Rotation Period Changes In Bp Starsmentioning

confidence: 93%

“…Hence, they have shown that the torsional surface oscillation, which results from the propagation of the torsional Alfvén wave, can provide a possible explanation for the observed period decrease (see also Stȩpień 1998). For other possible mechanisms, see discussions in Shultz et al (2019) and references therein.…”

Section: Rotation Period Changes In Bp Starsmentioning

confidence: 94%

“…Obviously, this is inconsistent with the prediction of the magnetic braking theory. Considering the high occurrence rate of spin-up, it is possible that the period derivative in σ Ori E may also change its sign in the future (Shultz et al 2019).…”

Section: Rotation Period Changes In Bp Starsmentioning

confidence: 99%

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Modeling of magneto-rotational stellar evolution

Takahashi

Langer

2021

A&A

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While magnetic fields have long been considered significant for the evolution of magnetic non-degenerate stars and compact stars, it has become clear in recent years that, in fact, all stars are deeply affected by their effects. This is particularly true regarding their internal angular momentum distribution, but magnetic fields may also influence internal mixing processes and even the fate of the star. We propose a new framework for stellar evolution simulations in which the interplay between magnetic field, rotation, mass loss, and changes in the stellar density and temperature distributions are treated self-consistently. For average large-scale stellar magnetic fields that are symmetric to the axis of the rotation of the star, we derive 1D evolution equations for the toroidal and poloidal components from the mean-field magnetohydrodynamic equation by applying Alfvén’s theorem; and, hence, a conservative form of the angular momentum transfer due to the Lorentz force is formulated. We implement our formalism into a numerical stellar evolution code and simulate the magneto-rotational evolution of 1.5 M⊙ stars. The Lorentz force aided by the Ω effect imposes torsional Alfvén waves propagating through the magnetized medium, leading to near-rigid rotation within the Alfvén timescale. Our models, with different initial spins and B-fields, can reproduce the main observed properties of Ap/Bp stars. Calculations that are extended to the red-giant regime show a pronounced core-envelope coupling, which are capable of reproducing the core and surface rotation periods already determined by asteroseismic observations.

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Section: Rotation Period Changes In Bp Starsmentioning

confidence: 93%

Section: Rotation Period Changes In Bp Starsmentioning

confidence: 94%

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Modeling of magneto-rotational stellar evolution

Takahashi

Langer

2021

A&A

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“…timescales of rotational period evolution observed in some helium peculiar stars (Mikulášek, et al 2008;Shultz, et al 2019), that cannot be explained by rotational braking by magnetized wind (Ud-Doula, Owocki & Townsend 2009). The stability considerations require that the star rotates along the axis with largest corresponding moment of inertia, that is, with helium-rich regions located around the poles.…”

Section: The Shape Of the Stellar Surfacementioning

confidence: 99%

Distorted surfaces of magnetic helium-peculiar stars: an application to a Cen

Krtička

Mikulášek

Prvák

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Helium-peculiar magnetic chemically peculiar stars show variations of helium abundance across their surfaces. As a result of associated atmospheric scale height variations, the stellar surface becomes distorted, with helium-rich regions dented inwards. Effectively, on top of flux variations due to opacity effects, the depressed helium-rich surface regions become less bright in the optical regions and brighter in the ultraviolet. We study the observational effects of the aspherical surface on the light curves of a Cen. We simulate the light curves of this star adopting surface distributions of He, N, O, Si, and Fe derived from Doppler mapping and introducing the effect of distortion proportional to helium abundance. We show that while most of the optical and UV variations of this star result from flux redistribution due to the non-uniform surface distributions of helium and iron, the reduction of light variations due to the helium-related surface distortion leads to a better agreement between simulated optical light curves and the light curves observed with the BRITE satellites.

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“…It is commonly assumed that as a result of their modulation by rotation, light curves of chemically peculiar stars can be typically reproduced using low-order harmonic expansion (e.g., Mikulášek et al 2007;Shultz et al 2019a). However, highprecision satellite photometry changed this picture.…”

Section: Introductionmentioning

confidence: 99%

Photometric signatures of corotating magnetospheres of hot stars governed by higher-order magnetic multipoles

Krticka,

Mikulasek,

Kurfurst

et al. 2022

Preprint

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Context. The light curves of magnetic, chemically peculiar stars typically show periodic variability due to surface spots that in most cases can be modeled by low-order harmonic expansion. However, high-precision satellite photometry reveals tiny complex features in the light curves of some of these stars that are difficult to explain as caused by a surface phenomenon under reasonable assumptions. These features might originate from light extinction in corotating magnetospheric clouds supported by a complex magnetic field dominated by higher-order multipoles. Aims. We aim to understand the photometric signatures of corotating magnetospheres that are governed by higher-order multipoles. Methods. We determined the location of magnetospheric clouds from the minima of the effective potential along the magnetic field lines for different orders of multipoles and their combination. From the derived magnetospheric density distribution, we calculated light curves accounting for absorption and subsequent emission of light. Results. For axisymmetric multipoles, the rigidly rotating magnetosphere model is able to explain the observed tiny features in the light curves only when the higher-order multipoles dominate the magnetic field not only at the stellar surface, but even at the Kepler radius. However, even a relatively weak nonaxisymmetric component leads to warping of equilibrium surfaces. This introduces structures that can explain the tiny features observed in the light curves of chemically peculiar stars. The light emission contributes to the light variability only if a significant fraction of light is absorbed in the magnetosphere.

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The accelerating rotation of the magnetic He-weak star HD 142990

Cited by 27 publications

References 60 publications

Modeling of magneto-rotational stellar evolution

Modeling of magneto-rotational stellar evolution

Distorted surfaces of magnetic helium-peculiar stars: an application to a Cen

Photometric signatures of corotating magnetospheres of hot stars governed by higher-order magnetic multipoles

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