Critical mass ratios, ﹩{q}_{\mathrm{cr}}﹩, for the onset of dynamical timescale mass transfer derived from different calculations. q is derived from the time-dependent calculation in Chen & Han (2008), ﹩{q}_{\mathrm{cr}}﹩ is derived from the adiabatic mass-loss calculation with same boundary condition as Chen & Han, ﹩{q}_{\mathrm{ad}}﹩ is derived from the adiabatic mass-loss calculation from stars with a standard mixing-length envelope, and ﹩{\tilde{q}}_{\mathrm{ad}}﹩ is derived from the adiabatic mass-loss calculation from stars with an isentropic envelope, which are presented as dots, a solid line, a dashed–dotted line, and a dashed line, respectively. ﹩{q}_{\mathrm{th}}﹩ for the onset of thermal timescale mass transfer derived from the thermal-equilibrium mass-loss model is shown by the thin dotted line. Black lines and red lines indicate the values of ﹩{q}_{\mathrm{cr}}﹩ from the RGB and AGB stellar models, respectively.