What is the period of low X-ray emission called ?
To explain the drop in X-ray emission across these dividing lines , a number of models have been proposed : low transition region densities , leading to low emission in coronae , high - density wind extinction of coronal emission , only cool coronal loops become stable , changes in a magnetic field structure to that an open topology , leading to a decrease of magnetically confined plasma , or changes in the magnetic dynamo character , leading to the disappearance of stellar fields leaving only small - scale , turbulence - generated fields among red giants .