Figure 11-11Pre–Main-Sequence Evolutionary Tracks This H-R diagram shows evolutionary tracks based on models of seven stars having different masses. The dashed lines indicate the stage reached after the indicated number of years of evolution. The birth line, shown in blue, is the location where each protostar stops accreting matter and becomes a pre– main-sequence star. Note that all tracks terminate on the main sequence at points that agree with the mass–luminosity relationship (see Figure 10-14a).