Influence of surface stressing on stellar coronae and winds

Abstract

The large-scale field of the Sun is well represented by its lowest energy (or potential) state. Recent observations, by comparison, reveal that many solar-type stars show large-scale surface magnetic fields that are highly non-potential - that is, they have been stressed above their lowest-energy state. This non-potential component of the surface field is neglected by current stellar wind models. The aim of this paper is to determine its effect on the coronal structure and wind. We use Zeeman-Doppler surface magnetograms of two stars - one with an almost potential, one with a non-potential surface field - to extrapolate a static model of the coronal structure for each star. We find that the stresses are carried almost exclusively in a band of uni-directional azimuthal field that is confined to mid-latitudes. Using this static solution as an initial state for an MHD wind model, we then find that the final state is determined primarily by the potential component of the surface magnetic field. The band of azimuthal field must be confined close to the stellar surface as it is not compatible with a steady-state wind. By artificially increasing the stellar rotation rate we demonstrate that the observed azimuthal fields can not be produced by the action of the wind but must be due to processes at or below the stellar surface. We conclude that the background winds of solar-like stars are largely unaffected by these highly-stressed surface fields. Nonetheless, the increased flare activity and associated coronal mass ejections that may be expected to accompany such highly-stressed fields may have a significant impact on any surrounding planets.

11 pages, 8 figures, accepted by Monthly Notices of the Royal Astronomical Society

References in corpus (4)

• The surprising magnetic topology of tauSco: fossil remnant or dynamo output?
• Large-scale magnetic topologies of late M dwarfs
• Large-scale magnetic topologies of early M dwarfs
• Toroidal versus poloidal magnetic fields in Sun-like stars: a rotation threshold

Cited by in corpus (35)

• Stellar magnetism: empirical trends with age and rotation
• M-dwarf stellar winds: the effects of realistic magnetic geometry on rotational evolution and planets
• Magnetic fields of M dwarfs
• On the environment surrounding close-in exoplanets
• Classical T Tauri stars: magnetic fields, coronae, and star-disc interactions
• Stellar Winds on the Main-Sequence I: Wind Model
• The energy budget of stellar magnetic fields
• Magnetic activity and hot Jupiters of young Suns: the weak-line T Tauri stars V819 Tau and V830 Tau
• The dependence of stellar mass and angular momentum losses on latitude and on active region and dipolar magnetic fields
• Magnetic fields of young solar twins
• Could a change in magnetic field geometry cause the break in the wind-activity relation?
• Observing the simulations: Applying ZDI to 3D non-potential magnetic field simulations
• Temporal variability of the wind from the star τ Boötis
• Characterisation of the HD 219134 multi-planet system I. Observations of stellar magnetism, wind, and high-energy flux
• Stellar Winds and Coronae of Low-mass Pop. II/III Stars
• Characterisation of stellar activity of M dwarfs. I. Long-timescale variability in a large sample and detection of new cycles
• Estimating stellar wind parameters from low-resolution magnetograms
• Magnetic field topology of tau Sco. The uniqueness problem of Stokes V ZDI inversions
• Magnetic topologies of young suns: The weak-line T Tauri stars TWA 6 and TWA 8A
• Magnetic field and prominences of the young, solar-like, ultra-rapid rotator V530 Per
• MOVES V. Modelling star-planet magnetic interactions of HD 189733
• Constraints on Magnetic Braking from the G8 Dwarf Stars 61 UMa and $\tau$ Cet
• The winds of young Solar-type stars in the Hyades
• The Effect of Magnetic Variability on Stellar Angular Momentum Loss II: The Sun, 61 Cygni A, $\epsilon$ Eridani, $\xi$ Bootis A and $\tau$ Bootis A
• The winds of young Solar-type stars in the Pleiades, AB Doradus, Columba and $\beta$ Pictoris
• Magnetic activity and radial velocity filtering of young Suns: The weak-line T Tauri stars Par 1379 and Par 2244
• How much do underestimated field strengths from Zeeman-Doppler imaging affect spin-down torque estimates?
• Magnetohydrostatic modelling of stellar coronae
• Starspots as the origin of ultrafast drifting radio bursts from an active M dwarf
• Stellar Coronal and Wind Models: Impact on Exoplanets
• The effects of stellar winds and magnetic fields on exoplanets
• Magnetic topologies of two weak-line T Tauri stars TAP 4 and TAP 40
• Winds of Planet Hosting Stars
• Surface activity of a Rossby sequence of cool Hyades stars
• The winds of young Solar-type stars in Coma Berenices and Hercules-Lyra