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.
Now, it's your turn to start classifying stars on your own.
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!
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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
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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? |
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