New Lab

Lab 6 - The Hertzsprung-Russell Diagram

One of the most useful tools for identifying star types in astronomy is the H-R Diagram. This idea, independently conceived in 1910 by Ejnar Hertzsprung and Henry Russell, is a graphical representation of intrinsic brightness as a function of temperature. It is largely based on this diagram that stars are classified.

There are a few variations of the H-R diagram:

• Absolute visual magnitude (Mv) vs. Spectral Type
• Absolute visual magnitude vs. Temperature
• Luminosity of star (sometimes given as relative to Sun’s luminosity) vs. Spectral Type
• Absolute visual magnitude vs. Color Index (B - V)

Other variations exist as well. The purpose and effect of each diagram is the same, however. Points plotted fall in limited regions on the graph, rather than in a wide distribution.

In today’s lab, you will plot an H-R diagram for the nearest and brightest stars, as given in the text appendices. Plot the Absolute visual magnitude (or Mv) versus the Spectral Type. Recall the Spectral Types are (in order of decreasing temperature):

O, B, A, F, G, K, M

Further, each of these can be subdivided into 10 categories, 0-9, though most of our stars today will be in the 0-5 range. Your graph will resemble the graph noted on the board in class.

Lab

Set up an H-R diagram for all of the brightest stars. y-axis (Absolute Visual Magnitude) should run from at least +16 to -7 (bottom to top), while the x-axis (Spectral Type) should include all classifications (and subdivisions) listed above. You may opt to include only those stars which are in subdivisions 0-5; this will eliminate a few stars.

Shade in the rough area which represents the Main Sequence of stars. Recall that this is a broad roughly diagonal band running from upper left to lower right.

Questions

1. How is temperature of a star determined?

2. What type of star is the sun?

3. What is another name for a dwarf star?

4. From the H-R diagram, identify stars which are giants.

5. Which of these are more likely to be supergiants?

6. Identify likely candidates for white dwarf stars.