Context :

Aims : We present a temperature and a magnetic-field surface map of the K2 subgiant of the active binary II Peg .
Employed are high resolution Stokes IV spectra obtained with the new Potsdam Echelle Polarimetric and Spectroscopic Instrument ( PEPSI ) at the Large Binocular Telescope ( LBT ) .

Methods : Fourteen average line profiles are inverted using our i Map code .
We have employed an iterative regularization scheme without the need of a penalty function and incorporate a physical 3D description of the surface field vector .
The spectral resolution of our data is 130 000 which converts to 20 resolution elements across the disk of II Peg .

Results : Our main result is that the temperature features on II Peg closely correlate with its magnetic field topology .
We find a warm spot ( 350 K warmer with respect to the effective temperature ) of positive polarity and radial field density of 1.1 kG coexisting with a cool spot ( 780 K cooler ) of negative polarity of 2 kG .
Several other cool features are reconstructed containing both polarities and with ( radial ) field densities of up to 2 kG .
The largest cool spot is reconstructed with a temperature contrast of 550 K , an area of almost 10 % of the visible hemisphere , and with a multipolar magnetic morphology .
A meridional and an azimuthal component of the field of up to \pm 500 G is detected in two surface regions between spots with strong radial fields but different polarities .
A force-free magnetic-field extrapolation suggests that the different polarities of cool spots and the positive polarity of warm spots are physically related through a system of coronal loops of typical height of \approx 2 R _ { \star } .
While the H \alpha line core and its red-side wing exhibit variations throughout all rotational phases , a major increase of blue-shifted H \alpha emission was seen for the phases when the warm spot is approaching the stellar central meridian indicating high-velocity mass motion within its loop .

Conclusions : Active stars such as II Peg can show coexisting cool and warm spots on the surface that we interpret resulting from two different formation mechanisms .
We explain the warm spots due to photospheric heating by a shock front from a siphon-type flow between regions of different polarities while the majority of the cool spots is likely formed due to the expected convective suppression like on the Sun .