The electron fraction for NSE with thermal weak equilibrium is shown by color contours for a range of densities and temperatures where NSE can be applied and which are relevant in different astrophysical scenarios. The solid black line shows the core-collapse trajectory for a 15 M_⊙ (A. Marek, priv. com.); the dashed lines represent the presupernova evolution of a 15 M_⊙ (black) and 25 M_⊙ (blue) stars; the red dashed lines represent a type Ia trajectory (F. Röpke, priv. com.); and the solid yellow lines correspond to the evolution of the proto-neutron star surface. Not all these scenarios will reach beta equilibrium and their electron fraction can therefore be different to the one shown here.