M67 (NGC 2682) is a very old open (or galactic) cluster in the constellation Cancer. Its age is estimated between 3-10 billion years with recent estimates of 4 billion years.
M67 is an interesting target for research in stellar evolution. Its Hertzsprung-Russell diagram, which compares color vs magnitude, displays numerous different stars along the various branches of evolution including red giants, hot blue spectral class A or F, bright K-type giants, and some strange stars near the bluer main sequence called Blue Stragglers.
M67 contains more than 500 stars. This cluster is estimated to be located 2,700 light years away. More information and additional images of this cluster can be found at the Messier Index - M67.
This image is an LRGB composite from multiple 15-second subexposures totaling 12.5, 10.75, 12, and 10.5 minutes respectively through a William Optics 4.3" f/7 refractor with an SXV-H9 detector using RGB filters. The image was taken on 5 March 2008.
As a project for my graduate class "Methods of Observational Astronomy," I used the data from the above image to create my own HR diagram of M67. I did this by using the blue filtered data and the green filtered data to measure color as B minus G and then plotted this against apparent magnitude (green data) for 885 stars in the image. The resultant plot is shown below.
In this plot can be seen the main sequence, the turnoff point where stars evolve off the main sequence and the red giant region. Compare this to the M67 HR plot from the Astrophysical Journal (ApJ 1955_121_616) below. To learn more about HR diagrams, see HR Diagram at Wikipedia.
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