LAB 06 - The HR Diagram

A quantity directly related to luminosity is magnitude, luminosity being the rate at which a star radiates electromagnetic energy into space (i.e., brightness). The APPARENT magnitude, denoted as m_v, corresponds to the brightness of a star as viewed from Earth. The ABSOLUTE magnitude of a star, denoted M_v is the magnitude a star would have if it were 10 parsecs from Earth (There are 3.26 light- years in a parsec).

When we plot the absolute magnitude vs. spectral type for various stars we generate a graph called the Hertzsprung-Russell (H-R) diagram. Once again, M_v vs. spectral type can be thought of as a comparison of absolute brightness (i.e. a representation of the star’s actual luminosity) to temperature (i.e. color).

It is found that most stars lie on or near a certain curve. This is the main sequence curve. Stars that lie on or near this curve are referred to as main sequence dwarfs. All main sequence dwarfs burn (via thermonuclear fusion reactions) hydrogen in their cores and are maintaining hydrostatic equilibrium.

It is important to remember that the star's position on the graph has no relation to its position in the heavens. We are plotting the two stellar properties LUMINOSITY and SURFACE TEMPERATURE and a myriad of information is to be obtained by pursuing these relationships. The following is a somewhat stylized version of the HR Diagram.  

In the image above, the Main Sequence is the roughly diagonal distribution of stars that starts with blue stars in the upper left and ends with red stars on the lower right.   

In this lab, you will construct an HR Diagram using some data from actual stars, then you will answer questions as part of an exploration of the features of the HR diagram.  

The following video provides you with an overview of how to construct the HR Diagram.  After you've watched the video, consult the steps in part 1 to access the graph and data you will need. 

Part 1 - Construct the HR Diagram

You will construct your diagram using the following blank HR Diagram graph paper: H-R DIAGRAM GRAPH.pdf. 

If you would prefer to print everything out and complete the graph off line, you can  access the graph, instructions, and data tables from this document as well: PHYS 1403 - H-R DIAGRAM LAB.pdf

Please note that the only thing you are going to turn in for this lab will be your completed graph.

Procedures

1. Plot all the stars in Table 2 onto the blank H-R diagram chart at the end of this lab packet.  Indicate the position of each star with an asterisk (*).

2. Once you’ve plotted all the stars from Table 2 onto the H-R diagram, connect each * with a dotted line to create a rough approximation of the path of the Main Sequence diagonally across the diagram.  Label this line as the Main Sequence.

3. Plot the stars from Table 3 onto the H-R diagram. Indicate each star’s position with a small circle. 

4. Once you’ve plotted all the stars from Table 3, circle them and label this region as Giant Stars.

5. Plot all the stars from Table 4 (M_v on the vertical scale and Spectral Type on the horizontal scale) onto your H-R diagram.  Mark each star’s position with a dot. Please note that Table 4 is a list of the brightest stars in the night sky.  

6. Now plot all the stars from Table 5 (again, M_v on the vertical scale and Spectral Type on the horizontal) onto your H-R diagram. Mark each star’s position with an X. Table 5 is a list of the 30 stars nearest the sun and the majority of these stars are considered to be the most common types of stars in the galaxy.  

Part 2 - Answer the Questions / Submit the Graph

Submit your graph and answer the questions to complete your lab.