Testing the Ability of Field Extrapolation Models to Predict the X-ray Emission Properties of Pre-Main Sequence Stars

Abstract

By extrapolating from observationally derived magnetic surface maps, obtained through Zeeman-Doppler imaging, models of stellar magnetospheres can be constructed. By assuming that the plasma trapped along the closed field lines is in hydrostatic equilibrium, coronal X-ray emission properties, such as the global X-ray emission measure and the amount of rotational modulation of X-ray emission, can be predicted. For pre-main sequence magnetospheres the analysis can be extended to incorporate accretion flows, and predict the amount of softer X-ray emission from accretion spots that would be observed. I will detail the preliminary results of an ambitious multi-wavelength, multi-observing site, and near contemporaneous campaign, combining spectroscopic optical, nIR, UV, X-ray (200ks, Chandra), spectropolarimetric and photometric monitoring of the accreting pre-main sequence star V2129 Oph. Surprisingly the new magnetic map derived from the 2009 data appears to indicate that the surface magnetic field has undergone little evolution since it was previously observed in 2005. The dataset also allows X-ray emission from the stellar corona and the accretion hotspots to be disentangled and crucially allows the validity, and the predictions, of the 3D field topologies derived via field extrapolation to be critically examined. SGG acknowledges support via an STFC Postdoctoral Fellowship.