Letters of Intent received in 2016

LoI 2018-1932
FM: Magnetic fields and related physics of B- and O-type stars

Topics

Observed properties of magnetic fields of B- and O-type stars
Structure of magnetic fields and magnetospheres of hot magnetic stars
Origin, generation and evolution of magnetic fields of hot stars
Physics of the wind-field interaction, including plasma/particle physics in hot-star magnetospheres (leading to radio emission, high-energy emission), magnetospheric mass balance and heating/cooling mechanisms
Interplay between magnetic fields and pulsations in hot stars, including synergies between spectropolarimetry and asteroseismology to probe internal dynamics
Influence of magnetic fields on evolution of hot stars, including modification of bulk rotation, wind quenchin, influence on internal transport of angular momentum and chemicals, consequences for nucleosynthesis, SN progenitors and the related yields, and role of magnetic fields in determining stellar end-states (e.g. (magnetic) white dwarfs, neutron stars and magnetars)
Magnetic fields of hot stars at the pre-main sequence and earlier formative stages
Signatures of fossil fields in wind-blown bubbles & SN remnants
Binarity and magnetism
New techniques/instruments/telescopes for measuring magnetic fields of hot stars

Rationale

Hot B- and O-type stars are the powerhouses of the Milky Way. Even before exploding as violent supernovae that seed the galaxy with heavy elements and help trigger new generations of star formation, their intense luminosity lights up and ionizes the nearby interstellar medium, and drives strong, high- speed stellar wind mass outflows. This mass loss, combined with rapid, sometimes near-critical stellar rotation, can exert a strong, even dominant influence on the formation and evolution of such hot stars, and on their demise as supernovae or GRB-producing hypernovae. But recent advances in observation and theory indicate a third agent – magnetic fields – can also play a key role. During recent years, advances in our observational, theoretical and numerical studies of stellar magnetism have led to significant advances in our understanding of this phenomenon:
- New generations of spectropolarimeters have revealed strong (∼kG), stable and ordered (typically dipole) magnetic fields in a growing subset of B- and O-type stars, establishing the incidence and characteristics of magnetic fields (their amplitude, their geometry, etc.) throughout a large range of stellar mass;
- The observational properties (chemical peculiarities, variability, emission, rotation) of newly-identified magnetic hot stars have been frequently found to be exotic and extreme, emphasizing the importance of magnetic fields in determining their rotational, atmosphere and wind properties;
- Semi-empirical and numerical hydrostatic, hydrodynamic and magnetohydrodynamical simulations have explored the dynamical interaction of such fields with rotation and mass loss in the stellar magnetosphere, in both 2 and 3 dimensions;
- Numerical simulations and theoretical calculations have examined the configurations and stability of interior magnetic fields, leading to the demonstration of the existence of stable large-scale internal field configurations, providing a physical basis for a fossil origin of the magnetic fields observed at the surfaces of hot stars, while 3-D numerical MHD simulations have been leveraged to understand the dynamics of magnetic fields both in hot stars' convective cores (dynamos) and in their radiative envelopes (fossil field relaxation) and their mutual coupling. The possibility of dynamos in stellar radiation zones, and in surface convection zones of evolved stars, has also been studied;
- Synergies between spectropolarimetric and asteroseismic observations (provided by the current generation of space-based photometric missions such as CoRoT, MOST and Kepler, and soon BRITE) have begun to provide a new view of the influence of the magnetic fields on stellar interior physics, including constraints on the transport of angular momentum and related mixing;
- The particular role of magnetic fields in binary systems has begun to be explored, including speculations concerning the generation of hot star magnetic fields in stellar mergers; Magnetic fields - identified in pre-main sequence B-type stars - are recognized as important agents modifying fragmentation in stellar formation. They are also a key actor that shapes the instability at the origin of the explosion of supernovae.
Notwithstanding these important advances, significant open questions remain concerning the origin, stability and evolution of the magnetic fields of hot stars, the basic physical processes implicated in the wind-field interaction, and the impact of magnetic fields on stellar structural, rotational and chemical evolution. We will therefore propose a 2 day Focus Meeting at the Vienna AGM in order to discuss outstanding issues, current activities and future efforts.