Figure 19-11: R I V U X G
Two Open Clusters The two clusters in this image, M35 and NGC 2158, lie in almost the same direction in the constellation Gemini. The nearer cluster, M35, has a number of luminous blue main-sequence stars with surface temperatures around 10,000 K as well as a few red giants. Hence, its H-R diagram resembles that shown in Figure 19-10g, and its age is around 100 million years (more accurately, around 150 million). The more distant cluster, NGC 2158, has no blue main-sequence stars; long ago, all of these massive stars came to the end of their main-sequence lifetimes and became giants. The H-R diagram for NGC 2158 is intermediate between Figure 19-10g and Figure 19-10h, and its age (1.05 billion years) is as well.
Two Open Clusters The two clusters in this image, M35 and NGC 2158, lie in almost the same direction in the constellation Gemini. The nearer cluster, M35, has a number of luminous blue main-sequence stars with surface temperatures around 10,000 K as well as a few red giants. Hence, its H-R diagram resembles that shown in Figure 19-10g, and its age is around 100 million years (more accurately, around 150 million). The more distant cluster, NGC 2158, has no blue main-sequence stars; long ago, all of these massive stars came to the end of their main-sequence lifetimes and became giants. The H-R diagram for NGC 2158 is intermediate between Figure 19-10g and Figure 19-10h, and its age (1.05 billion years) is as well.
(Jean-Charles Cuillandre (CFHT), © 2001 CFHT)