Are tides responsible for enhanced MG II emission in late-type binaries ?

Abstract

Mg II h and k fluxes are measured for a homogeneous sample of 30 G III and K III binaries. The spectra have been obtained from the IUE archive and calibrated in absolute units (erg cm^-2s^-1). Contrary to the generally accepted view that the rate of rotation is responsible for the enhanced chromospheric activity, the Mg II h and k fluxes correlate much better with parameters containing the separation of components in binary systems. It is suggested that the enhanced chromospheric emission in late-type giant binary systems is due to tides rather than to rotational velocities.