Ding, Anthony - COSMOS - UC Davis

H-R diagram of M29 8
Conclusion
Although it is a little bit off, the H-R diagram of M29 represents the typical H-R
diagram of a cluster of stars. The line of data points stretching from the bottom left to the
middle is what is known as the main sequence, where most of the stars are. The almost
vertical line branching out of the main sequence is known as the Red Giant branch. With
knowledge about these two branches, it is possible to estimate the age of M29. In order to
do this, it is necessary to locate a star just about to leave the main sequence and just about
to enter the Red Giant branch. In other words, we need to find the “turning point”. Once
we find the star, we need to convert that star’s B-V value into its temperature, and then
into its spectral type. Knowing its spectral type, we can then match the star up with a
table that compares a star’s spectral type to its average lifetime in the main sequence.
This estimated age is correct because the lifetime given is the lifetime in the main
sequence, and the star chosen is one just about to leave the main sequence. And since all
stars are born at the same time in a star cluster, we can say that the age of the star is
roughly equal to the age of the cluster. In the case of M29, the turn-off point is within an
approximate range of -0.09 to 0.1. Using a chart that matches temperature B-V values to
temperature (Sloan Digital Sky Survey n.d.), we know that this corresponds to a
temperature range of about 11,000K to 9,000K. Using another chart, we know that the
particular stars in the turning point range are spectral type B stars (Nave 2009). This tells
us that the star, and thus the cluster, is around 10 million to 100 million years old (Wilcox
2005). The actual estimated age of M29, using much more accurate data, is 10 milion
years old (Frommert and Kronberg 2007). The large range of 10 million to 100 million
calculated with the data from this paper is due to the fact that open clusters are spread out,