1999ApJ...518..873G

Models for the upper transition regions and coronae of the RS CVn binaries V711 Tau, AR Lac, and II Peg are presented. Empirical emission-measure distributions discussed in an associated paper are compared with those from theoretical models that assume an energy balance between optically thin radiative losses and conductive heating. The inadequacies of spherically symmetric, gravitationally bound models are highlighted, and this study focuses instead on energy-balance solutions in magnetic-loop geometries. The loop models reproduce the observed emission-measure distributions and electron densities using two families of structures. The hotter loops have peak temperatures of logT_e∼7.35 and heights of ∼0.05R_sstarf, whereas the cooler loops have peak temperatures of logT_e∼6.9 and heights of ∼0.15R_sstarf. The area coverage of the loops is consistent with photospheric spot patterns determined from photometry and Doppler imaging techniques, and the magnetic field strengths required to heat these loops agree with measured values. The ratio of conductive and radiative fluxes in the loop models are close to the value for a stable minimum energy-loss solution. Possible variations in the stellar Fe abundance, and their implications for the loop models, are also discussed.