EXors in the HR diagram. Filled and open circles represent embedded and classical EXors, respectively. Each source is plotted according to its quiescent luminosity and effective temperature. The upper, heavy dashed curve is the stellar birthline of Palla & Stahler (1990), and the lower, heavy solid curve is the zero-age main sequence. The lighter dashed curves are the pre-main-sequence evolutionary tracks of Palla & Stahler (1999). From right to left, the corresponding stellar masses, in solar units, are: 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.5, 2.0, 2.5, 3.0 and 3.5.