Age and Evolution (2) ...
The following figure summarizes the HR diagrams of a number of open clusters.
The left axis gives the absolute magnitude and the right axis calibrates the location of
the turnoff point with an age of the cluster. For example, the turnoff of the cluster M11
at absolute magnitude 1 suggests an age of several hundred
million years, but the turnoff of M67
near magnitude 4 indicates an age near 5 billion years (which is very old for an open
cluster).
As expected, we see evidence for a broad range of evolution among clusters of different ages.
The very young clusters like NGC 2362 are almost entirely main sequence, while the much older cluster M67 shows
extensive red giant evolution.
