Using Chandra/LETG spectra to probe stellar coronae

Abstract

We probe the relationship between surface magnetic fields and the X-ray emitting corona in the rapidly rotating star AB Dor. Circularly polarised spectra have been inverted to produce a surface (photospheric) magnetic field map. This surface map has been extrapolated to model AB Dor's coronal field topology and X-ray light curve. Chandra/LETG light curves of AB Dor from the same epoch show intrinsic variability at the 30% level. Period analysis indicates a fraction of this is due to rotational modulation. We measure velocity shifts in emission line centroids as a function of rotation period and find evidence of rotational modulation (max. vel. ~40+/- 13km/s). This modulation may indicate the presence of a localised X-ray emitting region at mid-to-high latitudes.