Torus-stable zone above starspots

Whilst intense solar flares are almost always accompanied by a coronal mass ejection (CME), reports on stellar CMEs rare, despite the frequent detection of 'super flares'. The torus instability magnetic flux ropes is believed to be one main driving mechanisms CMEs. Suppression instability, due confining background field that decreases sufficiently slowly with height, may contribute lack CME detection. Here we use as template estimate vertical extent this 'torus-stable zone' (TSZ) above active region. For an idealised potential model comprising fields local bipole (mimicking pair starspots) and global dipole, show upper bound TSZ increases size, dipole strength, source surface radius where becomes radial. boundaries depend interplay between spots' dipole's fields, which provide local- global-scale confinement, respectively. They range from about half size significant fraction radius. smaller spots intermediate field, secondary arises at higher altitude, increase likelihood 'failed eruptions'. Our results suggest low apparent occurrence rate cool stars is, least partially, presence extended TSZs.