  We have observed the flare star YY Gem simultaneously with XMM-Newton and
Chandra as part of a multi-wavelength campaign aiming at a study of variability
related to magnetic activity in this short-period eclipsing binary. Here we
report on the first results from the analysis of the X-ray spectrum. The
vicinity of the star provides high enough S/N in the CCD cameras onboard
XMM-Newton to allow for time-resolved spectroscopy. Since the data are acquired
simultaneously they allow for a cross-calibration check of the performance of
the XMM-Newton RGS and the LETGS on Chandra.
