AK Sco: enhanced magnetic activity in a pre-main sequence interacting binary

AK Sco is a unique source: a virgul10 Myr old premainsequence (PMS) spectroscopicbinary composed of two nearly equal F5 stars that at periastron are separated bybarely 11 stellar radii. The orbit is not yet circularized (e 0.47) and verystrong tides are expected. Previous high resolution UV spectroscopicobservations carried out with the HST/STIS have shown that there is an extendedregion with plasma at logTe (K)4.8 reaching 1.7R*. The magnetic diffusivity inthis region is very small; unusually strong tidally modulated polarimetricvariations of the system have been detected suggesting a strong coupling betweengravitational tides and the stellar field. We propose to study the variation ofthe Xray/UV spectrum of AK Sco as the stellar magnetospheres are modified by the tide. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]