Fig8_11 Globular star cluster in the H-R diagram

Fig8_11 Globular star cluster in the H-R diagram

Fig. 8.11 . The Hertzsprung-Russell diagram, abbreviated H-R diagram, for the globular star cluster M 5, where the absolute visual magnitude (left vertical axis) is plotted as a function of color index (bottom horizontal axis). It is very different from the H-R diagrams for open star clusters shown in Figure 8.9. The high mass stars in this globular star cluster have left the main sequences at a relatively low turn off point, denoted TO, indicating a greater age than the open star clusters, and it illustrates the evolutionary tracks of these stars into the red giant branch, designated RGB (top right), as well as other evolutionary stages such as the subgiant branch, denoted SGB, the asymptotic giant branch, designated AGB, and the horizontal branch, denoted HB, that extends to the left. The gap of missing stars in the horizontal branch for the globular star cluster M 5 shows the instability strip of pulsating stars, known as RR Lyrae stars. Halton Arp (1927- ) published the data shown in this diagram were in 1962 (Astrophysical Journal 135, 311 (1962).

Copyright 2010, Professor Kenneth R. Lang, Tufts University