Magnetic fields in non-convective regions of stars

Braithwaite, Jonathan; Spruit, H. C.

doi:10.1098/rsos.160271

Cited by 79 publications

(74 citation statements)

References 216 publications

(406 reference statements)

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“…The scenario commonly accepted to explain the origin of this magnetism is the fossil field theory. In this framework, magnetic fields observed at the surface of hot stars are proposed to be a remnant of magnetic fields amplified during an earlier evolutionary phase (Mestel 1999, or Braithwaite & Spruit 2017 for a review and the description of alternate theories).…”

Section: Introductionmentioning

confidence: 99%

Magnetic geometry and surface differential rotation of the bright Am star Alhena A

Blazère

Petit

Neiner

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Alhena A (γ Gem A) is a bright Am star, with the strongest disc-integrated magnetic field strength reported so far for an Am star. Its spectrum exhibits standard circularly polarized Zeeman signatures, contrary to all previously studied Am stars that display abnormal signatures dominated by a single-signed lobe.We present here the result of follow-up observations of Alhena, using very high signal-to-noise spectropolarimetric data obtained over 25 observing nights with NAR-VAL at Télescope Bernard Lyot, in the frame of the BRITE (BRIght Target Explorer) spectropolarimetric survey.We confirm that Alhena A is magnetic and we determine its surface magnetic properties using different methods. Inclined dipole models are used to reproduce the longitudinal field measurements, as well as the Stokes V line profiles themselves. In both cases, the model is consistent with a polar field strength of ∼ 30 G. This is confirmed by a Zeeman-Doppler Imaging (ZDI) model, which also unveils smaller scale magnetic structures. A rotational period of 8.975 days was identified using intensity line profile variations. The ZDI inversion suggests that the surface magnetic field is sheared by differential rotation, with a difference in rotation rate between high and low latitudes at about 15% of the solar value. This result challenges theories of the development of surface differential rotation in intermediate mass main sequence stars.

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Section: Introductionmentioning

confidence: 99%

Magnetic geometry and surface differential rotation of the bright Am star Alhena A

Blazère

Petit

Neiner

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…The evolution of fields and flows in the stable envelope, meanwhile, has been studied in simulations by Braithwaite and Spruit (2006) and follow-on papers, as described below; see review by Braithwaite and Spruit (2015). As discussed in Sect.…”

Section: Evolution Of Magnetism In Stable Layersmentioning

confidence: 99%

“…4.5, are usually thought to be of this type; similarly, the magnetic fields observed in white dwarfs and neutron stars, though perhaps produced at earlier stages of the star's evolution by dynamo action of some sort, are probably not today maintained by any dynamo process and are thus also in some sense "fossilized". Several recent reviews have discussed aspects of such fields; see, in particular, the recent review by Braithwaite and Spruit (2015) for an overview of field evolution in non-convective stars. We note here only a few brief points regarding the strengths such fields might reach, their stability over time, and some aspects of their appearance at the stellar surface.…”

Section: Fossil Fieldsmentioning

confidence: 99%

“…In this case, the surface field arises essentially as the end state of the instabilities described here (and in Sect. 4.5, and as reviewed recently in Braithwaite and Spruit 2015), interacting with rotation. (See Sect.…”

Section: Summary and Possible Implicationsmentioning

confidence: 99%

“…Images reproduced by permission from Braithwaite (2007) and Spruit (1999), copyright by ESO an Alfvén time (see Tayler 1973; Markey and Tayler 1973;Wright 1974;Flowers and Ruderman 1977;Acheson 1979;Pitts and Tayler 1985). A recent review is provided by Braithwaite and Spruit (2015). (To persist, the field must also be in dynamical equilibrium-i.e., all the forces acting on it must balance-but this is generically less difficult to arrange.…”

Section: Evolution and Stability Of Fieldsmentioning

confidence: 99%

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Magnetism, dynamo action and the solar-stellar connection

Brun

Browning

2017

Living Rev Sol Phys

252

182

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The Sun and other stars are magnetic: magnetism pervades their interiors and affects their evolution in a variety of ways. In the Sun, both the fields themselves and their influence on other phenomena can be uncovered in exquisite detail, but these observations sample only a moment in a single star's life. By turning to observations of other stars, and to theory and simulation, we may infer other aspects of the magnetism-e.g., its dependence on stellar age, mass, or rotation rate-that would be invisible from close study of the Sun alone. Here, we review observations and theory of magnetism in the Sun and other stars, with a partial focus on the "Solar-stellar connection": i.e., ways in which studies of other stars have influenced our understanding of the Sun and vice versa. We briefly review techniques by which magnetic fields can be measured (or their presence otherwise inferred) in stars, and then highlight some key observational findings uncovered by such measurements, focusing (in many cases) on those that offer particularly direct constraints on theories of how the fields are built and maintained. We turn then to a discussion of how the fields arise in different objects: first, we summarize some essential elements of convection and dynamo theory, including a very brief discussion of mean-field theory and related concepts. Next we turn to simulations of convection and magnetism in stellar interiors, highlighting both some peculiarities of field generation in different types of stars and some unifying physical processes that likely influence dynamo action in general. We conclude with a brief

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Solar structure and evolution

Christensen‐Dalsgaard

2021

Living Rev Sol Phys

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The Sun provides a critical benchmark for the general study of stellar structure and evolution. Also, knowledge about the internal properties of the Sun is important for the understanding of solar atmospheric phenomena, including the solar magnetic cycle. Here I provide a brief overview of the theory of stellar structure and evolution, including the physical processes and parameters that are involved. This is followed by a discussion of solar evolution, extending from the birth to the latest stages. As a background for the interpretation of observations related to the solar interior I provide a rather extensive analysis of the sensitivity of solar models to the assumptions underlying their calculation. I then discuss the detailed information about the solar interior that has become available through helioseismic investigations and the detection of solar neutrinos, with further constraints provided by the observed abundances of the lightest elements. Revisions in the determination of the solar surface abundances have led to increased discrepancies, discussed in some detail, between the observational inferences and solar models. I finally briefly address the relation of the Sun to other similar stars and the prospects for asteroseismic investigations of stellar structure and evolution.

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Magnetic fields in non-convective regions of stars

Cited by 79 publications

References 216 publications

Magnetic geometry and surface differential rotation of the bright Am star Alhena A

Magnetic geometry and surface differential rotation of the bright Am star Alhena A

Magnetism, dynamo action and the solar-stellar connection

Solar structure and evolution

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