Coronal structure of the cTTS V2129 Oph
arXiv:0802.2213 · doi:10.1111/j.1365-2966.2008.13103.x
Abstract
The nature of the magnetic coupling between T Tauri stars and their disks determines not only the mass accretion process but possibly the spin evolution of the central star. We have taken a recently-published surface magnetogram of one moderately-accreting T Tauri star (V2129 Oph) and used it to extrapolate the geometry of its large-scale field. We determine the structure of the open (wind-bearing) field lines, the closed (X-ray bright) field lines and those potentially accreting field lines that pass through the equatorial plane inside the Keplerian co-rotation radius. We consider a series of models in which the stellar magnetic field is opened up by the outward pressure of the hot coronal gas at a range of radii. As this radius is increased, accretion takes place along simpler field structures and impacts on fewer sites at the stellar surface. This is consistent with the observed variation in the Ca II IRT and HeI lines which suggests that accretion in the visible hemisphere is confined to a single high-latitude spot. By determining the density and velocity of the accretion flows, we find that in order to have most of the total mass accretion rate impacting on a single high-latitude region we need disk material to accrete from approximately 7R*, close to the Keplerian co-rotation radius at 6.8R*. We also calculate the coronal density and X-ray emission measure. We find that both the magnitude and rotational modulation of the emission measure increase as the source surface is increased. For the field structure of V2129 Oph which is dominantly octupolar, the emission forms a bright, high-latitude ring that is always in view as the star rotates. Since the accretion funnels are not dense enough to cause significant scattering of coronal X-ray photons, they provide only a low rotational modulation of around 10% at most.
10 pages, 9 figures
References in corpus (8)
- The Magnetic Fields of Classical T Tauri Stars
- Magnetic fields and accretion flows on the classical T Tauri star V2129 Oph
- Accretion to Stars with Non-dipole Magnetic Fields
- The coronal structure of AB Dor determined from contemporaneous Doppler imaging and X-ray spectroscopy
- T Tauri stellar magnetic fields: He I measurements
- Why are accreting T Tauri stars observed to be less luminous in X-rays than non-accretors?
- Spectropolarimetry of the Classical T Tauri Star TW Hydrae
- CaII Infrared triplet line models in Classical T Tauri stars