Astronomy lab

Observing Properties of Star Clusters

Big Idea: Star clusters have properties that can be observed and categorized.

Goal: Students will conduct a series of inquiries about the nature of features of star clusters.

Computer Setup:

Go to http://www.rc-astro.com/clusters.php

Phase I: Exploration

What are the two types of clusters that are shown?

___________________ and _________________________

Read through this page on Color Index (B-V) and temperature: http://www.astronomynotes.com/starprop/s5.htm

Note: We can assume that all the stars in a given cluster are approximately the same distance away from the Earth.

Phase II – Does the Evidence Match the Conclusion?

1) Enlarge and examine several of the images of the two different types of clusters at the website: http://www.rc-astro.com/clusters.php

2) Note similarities and differences between the two different types.

3) If a student proposed a generalization that “Globular Clusters generally contain fewer stars than open clusters,” would you agree or disagree with the generalization based on the evidence you collected? Explain your reasoning and provide specific evidence either from the above questions or from evidence you generate from the photos.

Phase III – What Conclusions Can You Draw From the Evidence?

A student decided to look for a relationship between the temperatures of the brightest stars seen in a typical globular cluster compared to a typical open cluster. What conclusions and generalizations can you make from the following data collected by a student? Explain your reasoning and provide specific evidence, with sketches if necessary, to support your reasoning.

Note: The filter combination we will use is B-V: the difference between the star's brightness in a blue filter and in a yellow filter. The important thing to know is that the bigger B-V is the redder the star is -- and the smaller it is (including negative values), the bluer the star.

Table 1: Data for 47 Tuc (Globular Cluster) and M45 (Open Cluster)

47 Tuc

M45

Star Number	Magnitude	Color (B-V)		Star Number	Magnitude	Color (B-V)
10012	19.6	0.76		133	14.4	1.28
10170	20.6	0.98		165	7.6	0.12
10200	21	1.05		345	11.6	0.84
10206	21	0.96		522	11.9	0.9
10278	21.6	1.23		697	8.6	0.35
10335	22	1.31		804	7.9	0.2
10359	22.2	1.23		950	4.2	-0.1
10489	22.6	1.33		1040	15.8	1.44
10610	23	1.45		1103	14.8	1.47
20028	17.6	0.53		1234	6.8	0.02
20034	17.7	0.58		1266	8.3	0.36
20049	18	0.57		1305	13.5	1.18
20070	18.4	0.6		1309	9.5	0.47
20104	18.8	0.65		1355	14	1.23
20130	19.1	0.69		1432	2.9	-0.09
20185	19.8	0.83		1454	12.8	1.16
20210	20.1	0.88		1516	14	1.31
20239	20.4	0.93		1766	9.1	0.47
20335	21.4	1.1		1797	10.1	0.56
20364	21.6	1.2		1924	10.3	0.62
30014	13.5	1.1		2168	3.6	-0.08
30103	15.5	0.82		2181	5.1	-0.08
40002	12	1.45		2209	14.4	1.47
40022	12.6	1.25		2406	11.1	0.76
40043	12.9	1.14		2425	6.2	-0.05
40130	14	0.99		2588	13.1	1.22
40135	14	0.69		2601	15	1.55
40144	14	0.79		2655	15.5	1.36
40164	14	0.59		2870	12.5	1.07
40351	14.9	0.85		2881	11.8	0.86
40628	16.2	0.73
40821	16.6	0.73
41051	16.9	0.7
41107	17	0.58
41456	17.2	0.51

4) Evidence-based Conclusion:

Phase IV – What Evidence Do You Need?

Go to: http://www.unm.edu/~astro1/101lab/lab10/lab10_E.html

Click “Stellar Evolution Simulation.”

Add “100 stars.” All of these should initially be on the Zero-Age Main Sequence.

Click “Evolve.”

Watch the simulation. Pay particular attention to the age in the bottom left corner.

Additional information

Table 2: Main Sequence Lifetimes

Spectral Type	Color B-V	Lifetime (years)
O	-0.4	< 106
B	-0.2	3 X 107
A	0.2	4 X 108
F	0.5	4 X 109
G	0.7	1 X 1010
K	1	6 X 1010
M	1.6	>1011

Describe precisely what evidence you would need to collect in order to answer the research question of, “If all of the stars in a given cluster are formed out of the same nebula, how can the age of that cluster of stars be determined?”

5) Create a detailed, step-by-step description of evidence that needs to be collected and a complete explanation of how this could be done—not just “graph the stars on the HR-diagram and look,” but exactly what would someone need to do, step-by-step, to accomplish this. You might include a table and sketches-the goal is to be precise and detailed enough that someone else could follow your procedure. Note: You do not need to actually take this data for this phase.

Phase V – Formulate a Question, Pursue Evidence, and Justify Your Conclusion

Your task is design an answerable research question, propose a plan to pursue evidence, collect data using the information given in the lab or on the websites presented and create an evidence-based conclusion about some relationship of star clusters that you have not completed before.

Research Report:

6) Specific Research Question:

7) Step-by-Step Procedure, with Sketches if Needed, to Collect Evidence:

8) Data Table and/or Results:

9) Evidence-based Conclusion Statement:

Phase VI – Summary PRINT YOUR NAME

10) Create a 50-word summary, in your own words, that describes the features in star clusters. You should cite specific evidence you have collected in your description, not describe what you have learned in class or elsewhere. Feel free to create and label sketches to illustrate your response.