The Coronal Structure of Ab Doradus

Abstract

We perform a numerical simulation of the corona of the young, rapidly rotating K0 dwarf AB Doradus using a global MHD model. The model is driven by a surface map of the radial magnetic field constructed using Zeeman-Doppler Imaging. We find that the global structure of the stellar corona is dominated by strong azimuthal tangling of the magnetic field due to the rapid rotation. The MHD solution enables us to calculate realistic Alfvén surfaces and we can therefore estimate the stellar mass loss rate and angular momentum loss rate without making undue theoretical simplifications. We consider three cases, parameterized by the base density of the corona, that span the range of possible solutions for the system. We find that overall, the mass and angular-momentum loss rates are higher than in the solar case; the mass loss rates are 10 to 500 times higher, and the angular momentum loss rate can be up to 3 × 10 4 higher than present day solar values. Our simulations show that this model can be use to constrain the wide parameter space of stellar systems. It also shows that an MHD approach can provide more information about the physical system over the commonly used potential field extrapolation.

The Effect of Combined Magnetic Geometries on Thermally Driven Winds. I. Interaction of Dipolar and Quadrupolar Fields

“…The dependence of the Alfvén radius and opening radius on field geometry and magnetisation is a constraint on PFSS models, which are readily used with ZDI observations as a less computationally expensive alternative to MHD modelling (Jardine et al 1999(Jardine et al , 2002Dunstone et al 2008;Cohen et al 2010;Johnstone et al 2010;Rosén et al 2015;Réville et al 2015b). PFSS models are a useful tool, however require the source surface radius, R ss , as an input.…”

T Tauri star magnetic fields and magnetospheres

“…At slow rotation rates, fields weaken and large scale fields are largely poloidal and axisymmetric for G and K-type stars (see review by Donati & Landstreet 2009). These surface magnetic field maps can be extrapolated to model the coronal topology of active cool stars and predict the properties of their X-ray coronae Gregory et al 2007) and the detailed structure of stellar winds (e.g., Cohen et al 2010;Vidotto et al 2011). …”

Masses and activity of AB Doradus B a/b

“…AB Dor A is one of the closest, brightest, and most intensively studied highly active stars, see, e.g., Cohen et al (2010) for an extensive list of references. In November 2009 we performed a multiwavelength study of the AB Dor system.…”