The purpose of this lab assignment is to teach you how the H-R diagram was made, and to learn what it tells us. You will be making two H-R diagrams and comparing them.
| H-R diagram for nearby stars | 2 points |
| H-R diagram for bright stars | 2 points |
| Bar graph of number vs magnitude for nearby stars | 1.5 points |
| Bar graph of number vs magnitude for bright stars | 1.5 points |
| Answers to 3 follow-up questions | 1 point each |
| Tuesday May 18 - Thursday May 20 | 2 points |
| Thursday May 20 - Tuesday May 25 | 4 points |
| Tuesday May 25 - Thursday May 27 | 6 points |
| Thursday May 27 - Tuesday June 1 | 8 points |
There isn't a class meeting on June 1. You may turn in your lab until the end of Linda's section (4:30 PM) on June 1. The deadline on each day other than June 1 is 2 PM, or immediately after you come into the classroom. The rules about handing in labs at the beginning of class and valid excuses for late labs are the same as for Lab 1.
You will be making two H-R diagrams for this lab. First, make one for the nearby stars list.
You should give us the following, with your name on each page:
You MUST turn in a hardcopy of everything. The TA's will not look at diagrams or answers to questions posted on the Web, emailed to us, or in any form except a paper copy.
All parts of your project must be submitted at the same time. If you turn in an incomplete lab, you may not turn the rest of it in later, even if you submit all of the parts before the due date.
Whenever you turn in your lab, make sure we actually get it. Don't slip it under our doors, leave it on our desks, put it in our mailboxes, or give it to our office-mates.
To make your diagrams easier for your TA's to read and grade (we remind you that TA's do have the right to deduct points for difficult-to-read diagrams!), you should follow these guidelines:
Hint: Use your bar graphs to help you answer questions 1 and 2. Think about what the bar graph for the stars used to make the standard H-R diagram might look like.
When you're making your diagram, especially if you're using your own paper, do a few "sanity checks." Try plotting a star by its temperature and luminosity, then plot the same star again by its magnitude and spectral type. If it doesn't come out in the same place, you know you're doing something wrong. If this keeps happening and you can't figure out why, come see one of us.
One problem may be that the axes are labelled in a somewhat "funny" way. Remember, the high temperatures are on the left side of the diagram, and also that lower magnitudes correspond to higher luminosities. All H-R diagrams that I've seen are like this. We have the ancient Greeks to blame for the magnitudes running backwards- they concocted a scheme of ranking star brightnesses in which the brightest stars were called first magnitude, the next brightest second magnitude, and so on. I don't know who started the tradition of plotting the high temperatures on the left.
When you make your H-R diagram for the bright star list, you may find that some stars are "off the chart"- they are hotter than the hottest temperature on the chart. That's supposed to happen. You may either plot the stars to the left of the chart, or write on the chart (or on a separate piece of paper) a list of stars that were too hot to include on the chart.
The standard H-R diagram is a plot that includes all of the different kinds of stars. A perfect H-R diagram would include every star that has ever existed, at every phase of its life. Obviously, that's impossible, so what astronomers do is observe a large sample of stars. However, there are a few problems with this approach:
Most of you will probably find this lab assignment more difficult than the first one. It will probably take longer to complete, so you should start early.
