Beginning Ideas/ Questions: Name: [ ] Lab: Determining Distances and Ages of Star Clusters? 1. How do we use distance modulus to determine the distance to star clusters? 2.. 3. Background Information:. 4...... Complete the following table then use the space to the right to explain how the size of distance modulus can be used to predict distance. Use specific examples from the table in your response. Object Apparent Magnitude m Absolute Magnitude M Distance Modulus m-m Distance (pc) Star A 2.4 10 Star B 5 16 Star C 10 25 Star D 8.5 0.5...
Part A Procedure: 1. Open up the Cluster Fitting Explorer. Note that the main sequence data for nearby stars whose distances are known are plotted by absolute magnitude in red on the HR Diagram. 2. In the Cluster Selection Panel, choose the Pleiades cluster. The Pleiades data are then added in apparent magnitude in blue. Note that the two y-axes are aligned, but the two main sequences don t overlap due to the distance of the Pleiades (since it is not 10 parsecs away). 3. Move the cursor into the HR diagram, the cursor will change to a handle, and you can shift the apparent magnitude scale by clicking and dragging. Grab the cluster data and drag it until the two main sequences are best overlapped. We can now relate the two y-axes. 4. Check show horizontal bar which will automate the process of determining the offset between the m and M axes. Note that it doesn t matter where you compare the m and M values, at all points they will give the proper distance modulus. 5. Fill in Table 1 by following the procedure above and using the Distance Modulus Calculator on that page to find distances. During Procedure Questions 6. Q1: Left vertical axis is used to represent...., right vertical axis is used to represent. and, the red diagonal line most likely represents Q2: Are stars in Pleiades cluster brighter or dimmer than what we are expected to see according to the main sequence? Explain how you knew this based on the appearance of the HR Diagram. Q3: As you move the cluster data. What variable(s) about the stars remain the same? Q4: Stars that are mostly missing in Pleaides cluster are main sequence stars / red giants / blue giants / white dwarfs. (Circle all that apply.) Q5: Fill in the corresponding values using the horizontal bar: M m - 3.4 19.5 0 Q6: Since absolute magnitude is brighter than apparent magnitude in Pleiades, that means that Pleaides is than 10 pc. Data and Observations: Table 1 Title: Design a data table that can hold data such as both magnitudes, distance modulus and distances. Include all needed details.
Part B Procedure: 1. Transfer the distance modulus data from Table 1 into Table 2 2. In the Cluster Selection Panel, choose the Pleiades cluster. Align the cluster data with the main sequence. 3. Determine the absolute magnitude of a star at the turn-off point. Record in column M TO. 4. Using Figure 1 provided on this page, estimate the approximate age of the cluster. 5. Using internet look up the age of each cluster by using Google and search terms such as Age of Hyades star cluster 6. Calculate percent error between your During Procedure Questions Q1: What is the turn-off point on the main sequence? What does it mean?.. Q2: Sketch HR-Diagram and label the turn off point. measurements and actual age of the cluster. Q3: Look up the formula for percent error and record it below: Data and Observations Table 2 Title: Cluster Name M TO Measured Age (years) Actual Age (years) % Error Figure 1: Absolute Magnitude and Lifetime Relationship
Analysis: 1. Create a scatter plot graph of distance modulus vs distance using Table 1. Draw a best-fit line for your data. Label clusters or make a key. Describe the graph completely. Fill the space below. Be detailed and describe any patterns or relationships you notice in the data. 2. Create a scatter-plot graph of measured cluster ages and actual ages vs distance modulus using Table 2. Describe the graph completely. Fill the space below. Be detailed and describe any patterns or relationships you notice in the data.
Conclusions: 1. In Pleiades Cluster there are several stars that are above the main sequence in the upper left. Explain reasons why these stars are not on the main sequence? What is their likely stage of life? 2. In Pleiades Cluster there are several stars that are below the main sequence especially near temperature of about 5,000K. Explain why these stars are not on their main sequence? What is their likely stage of life? 3. Describe how the shape of the H-R Diagram for a cluster changes as the cluster ages. If necessary sketch out H-R diagram to aid in making your explanation. 4. Which cluster had the biggest error according to your calculations? View the H-R Diagram of that cluster again and give at least 2 reasons for potential cause of this. 5. The H-R diagram of a Coma cluster shows a star at turn-off point whose absolute magnitude is 1. Predict the age of the Coma clusters and explain how you made that prediction. 6. Star cluster NGC 752 has an absolute magnitude of 22 and apparent magnitude of 34. Predict its distance. Explain how