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# Identifying the Spectral Types of Stars

So, what type of star did you think it was? The star had all the hydrogen lines, so that narrows our choices down to B, A, and F. However, it had no helium lines, so that rules out a type B star. The star did have ionized calcium (the H and K lines), which are found in type F stars. So the star is a type F star. The star whose spectrum you identified is shown to the right. (The picture shows two stars close together; the star you identified is the larger one on the bottom left.)

As you can see, classifying stars is a little logic puzzle.

Exercise 2. Use the Object Explorer to look at spectra of the stars in the table below. Remember to click on the Fiber number, then click on "Spectrum" in the Object Explorer.

 Plate Fiber 266/51630 483 294/51986 623 266/51630 394 297/51959 316 266/51630 344 273/51957 391 282/51658 527 281/51614 398 268/51633 66 310/51990 178

Classify the stars according to their spectra (note: one or two of the objects are labeled as "huh" instead of "star." These objects have since been identified as stars, and their spectral types have been determined). Some spectral types may appear more than once. There is not necessarily one star of each spectral type. Be careful...some of the spectral types are hard to tell apart!

 Exercise 3. Use the Get Plates tool to choose about a dozen stars from the SkyServer database. Choose any plate you like from the "Plate" dropdown menu, then click on one of the "star" links to see a star's spectrum. Determine the spectral type of each star. Your sample is probably too small to ensure you will find a star of each type, but try to find at least one example of most spectral types. You will probably look at 20-30 stars. Launch the Get Plates tool

 Exercise 4. On the board, make a histogram showing the data from Exercise 3 for everyone in the class. Let the bins represent the spectral types (OBAFGKM). When you make the class histogram, label each square with the star's plate number and fiber number. There are a couple of reasons to label the squares. You don't want to count the same star twice. It is also possible that two groups analyzed the same star and disagree on its type. If that happens, ask the rest of the class check the findings! Which types of stars are most common? Which types of stars are least common?

 Question 7. You may have noticed that type O stars are rare, especially in the SDSS database. Why do you think we see so few of them?

 Question 8. Did you find any stars that did not fit into any of the spectral types? If so, what were their characteristics?