Fig8_9 Open star clusters in the H-R diagram

Fig8_9 Open star clusters in the H-R diagram

Fig. 8.9 . The open star clusters are relatively young, and most of their stars have not yet left the main sequence in the Hertzsprung-Russell, abbreviated H-R, diagram. The youngest clusters, such as the Pleiades, retain all but the topmost part of the main sequence. The turn off point of the Pleiades star cluster from the main sequence indicates an age of roughly 100 million years. The Hyades star cluster, which turns off about halfway down the main sequence, is about 600 million years old. The lowest open cluster in this diagram, M67, is an estimated 5 billion years old, with a main sequence that stops just above the Sun. One globular star cluster, M3, is shown for comparison. Alan Sandage (1926-2010) first published this diagram in 1957 (Astrophysical Journal 126, 326 (1957)).

Copyright 2010, Professor Kenneth R. Lang, Tufts University