(a) Hydrogen mass fraction at ignition (X_H,ign) as a function of accreted hydrogen fraction (X_H,acc) for various accretion rates (﹩\dot{m}﹩) and two metallicities. Circular markers indicate Z = 0.02, while square markers indicate Z = 0.01. Different colors correspond to different values of ﹩\dot{m}/{\dot{m}}_{{\rm{Edd}}}﹩. (b) Ignition column depth versus hydrogen mass fraction at ignition for two metallicities.