Actually, IIRC, for a type 2 its less dependant on the mass of the star, but on the strength of the internal pressure from the core, in the form of thermonuclear radiant energy causing expansion. If the Shivans' subspace weapon could disrupt all thermonuclear activety in the Cappelean sun at the same time, this expansive force would cease, causing the gravity of the star to collapse it in towards itself. While thermonuclear activitey would cease, the synthesis of nutronium from electrons and protons that occurs when the core exceeds 1.2 solar masses might still occur, resulting in the massive energy release in the form of a supernova.
