Doppler imaging of stellar surface structure. XIX. The solar-type components of the close binary sigma2 Coronae Borealis
We present the first Doppler image for both stellar components of the F9+G0 ZAMS binary sigma 2 CrB and found evidence for the coexistence of cool and warm spots on both stars. Cool spots appear mainly at polar or high latitudes while a confined equatorial warm belt appears on the trailing hemisphere of each of the two stars with respect to the orbital motion. We also present an update of the TempMap imaging code that allows us to solve the stellar surface temperature distribution on both binary components simultaneously, including photometric input. Several test reconstructions are performed to demonstrate its reliability and robustness. Our new orbital solution results in very precise masses for both components - good to 0.4% - and confirms the spectral classifications of F9 and G0 for the primary and secondary, respectively. The visual component, sigma 1 CrB, seems to be G4 rather than G0. All three components are on or very close to the ZAMS which is also confirmed by the relatively high lithium abundance of about twenty times the solar abundance. Photometric light variations are detected with a period of 1.157+/- 0.002 days that we interpret to be the rotation period of both binary components. A 0\fm04 dimming in y together with a reddening of 0\fm01 in b-y during the year 2000 suggests a long-term spot variability compatible with a period of at least 260 days.