evolutionary track

The term evolutionary track is used for the track across a H-R diagram plotting a star's changes over its lifetime. (The term stellar evolution indicates such changes of a single star, or a single type of star, rather than the "biological" sense of evolution regarding how successive generations differ; perhaps the phrase aging track would be less misleading.) An evolutionary track can be plotted as a curved line from a point plotted for the star at some point in its life (presumably early in its life, such as when it enters its main-sequence phase), leading to a later point in its life (e.g., its core collapse supernova). It might at some point enter the H-R diagram's red-giant region and possibly its asymptotic giant branch (AGB) region. The track depends largely upon the mass of the star as well as its metallicity, though the possible tracks of interacting binaries are undoubtedly so numerous that only certain specific cases are worked out to much extent. Hayashi tracks are a set of evolutionary tracks calculated for the pre-main-sequence star (PMS) phase.