Assignment 6: Ages of Stellar Clusters

Due: Before 5 pm Tuesday, November 28, 2006. Please turn in hardcopy.

Hubble Space Telescope image of the globular cluster M80

1. Below is the typical Hertzsprung-Russell diagram for the globular cluster M55 (Mochejska, APOD). What is a globular cluster? Identify the stars in the various regions of the Hertzsprung-Russell diagram. The blue stars in the upper left are known as Blue Stragglers

2. Use the the following figures to estimate the age of M55. The figures are based on theoretical calculations of stellar clusters of various ages. The age of the cluster is determined by the turn-off point of the cluster. Mark the turn-off point on the Hertzprung-Russell diagram. What is the approximate luminosity and surface temperature of the stars near the turn-off point?

The figures are theoretical Herztsprung-Russell diagrams. Use them to estimate the age of M55. The abbreviations are 1 Myr = 1 million years and 1 Gyr = 1 billion years. Make an estimate as to how accurate you believe your answer to be.

3. Find the age of the cluster whose Hertzsprung-Russell diagram is shown below. Mark the turn-off point on the Hertzsprung-Russell diagram. What is the approximate luminosity surface temperature of stars near the turn-off point?