ASSIGNMENT #9
Due Wednesday, October 31, at 9:00 a.m.
- Plot an H-R diagram for the stars listed below. (The temperatures are given in kelvins, the masses in solar masses, and the luminosities in solar luminosities.) Plot log (L /L
) as a function of log (T) with T in kelvins and with T increasing to the left. If all of your values of log T are in a narrow range, make the ends of that range the limits of your horizontal axis. Your graph, with a dot for each star, should look something like the H-R diagrams in the book and on the web. Label your points with the names of the stars (the first is named A, etc.) Be sure to label your axes. Do not connect the dots with a line. Use graph paper unless you produce a computer-generated plot. No hand sketches!
- Which stars do you think are main sequence? white dwarfs? red giants?
- Plot a graph of log (L/L) vs. log (M/M) for the main sequence stars. This time both quantities should increase in the conventional order: log M/M to the right and log (L/L) upward. Then draw a straight line that is a reasonably good fit to the points. What is the slope of this line?
You may use a calculator, either your own or one on the web, to obtain the logs and plot points on graph paper, or you may use a spreadsheet to do all or part of the work for you. If you use a spreadsheet, download the text document HW09Stars.txt, save it as text, and then open it with the spreadsheet. Warning: It is difficult, but not impossible, to find out how to get Excel to make a plot with the horizontal axis increasing to the left.
Some places to look for help:
- Graphing Resources (North Carolina State University)
- Graphing Equations and Inequalities (math.com)
- An example of the use of a log-log plot (University College, London)
| Star | Temp | M/M | L/L |
| A | 30500 | 16.6 | 28200 |
| B | 4000 | 10 | 150000 |
| C | 21900 | 9.12 | 3890 |
| D | 16600 | 5.25 | 790 |
| E | 9020 | 2.4 | 36.3 |
| F | 8220 | 2.04 | 18.2 |
| G | 6920 | 1.7 | 13.2 |
| H | 6310 | 1.51 | 7.24 |
| I | 5860 | 1 | 1.23 |
| J | 3770 | 0.59 | 0.0741 |
| K | 15000 | 0.41 | 0.01 |
| L | 3160 | 0.24 | 0.0069 |
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