Other Spectral Types
The spectral types you have used, OBAFGKM, were developed in the
early 20th century. In the last ten years, a new generation of
telescopes has been built. These telescopes include the
Hubble Space Telescope, the giant
Keck Telescopes in Hawaii,
Gemini
North and Gemini South, the
Very Large Telescope in Chile,
the Subaru Telescope, and
several others. The CCD cameras in the telescopes have also gotten much more
sensitive. These
advances have allowed astronomers to discover new types of stars
that do not fit into any of the traditional spectral classes.
Type C stars, or carbon stars, are stars unusually rich in carbon.
They have a beautiful, deep red color when viewed through a telescope. They
appear red because a variety of carbon compounds on their surface absorb most
of their blue light. The spectrum below comes from a type C star
found by SDSS.
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Click on the image to see it full size |
Type L and type T stars are cooler, smaller, and dimmer than type M
stars. They are usually very faint and difficult to find, and it's
hard to obtain spectra from them.
Type W stars, also known as Wolf-Rayet stars, are
as hot as the type O stars, but they have strong emission lines due to
clouds of gas surrounding the star.
Type S stars are very rare. They are similar to type M stars
except with zirconium oxide and lanthanum oxide instead of titanium oxide.
Most stars you observe will have one of the traditional spectral types.
However, you may occasionally run across one of the unusual types listed
here. Every star's spectrum is unique, much like a human
fingerprint. When a star is close to the boundary between two types,
it can be difficult to classify by simply looking at the spectrum.
Look at the star spectra in the exercises below. In each exercise,
click the Fiber number to launch the Object Explorer.
Exercise 5. Use the Object Explorer to examine
Plate 282/51658, Fiber
345. This star is a class C carbon star.
What spectral lines are present? Are the spectral lines present
that you cannot identify from the charts given earlier?
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Exercise 6. Repeat Exercise 5 for Plate 282/51658, Fiber
370. This is a sub-dwarf star. What is its spectral type (if you can
classify it)? |
Exercise 7.
Look at the stars below. These stars have interesting spectra that are
difficult to classify. As you can see, not every star fits
neatly into our classification system!
What absorption lines are present? Do they fit into one of our
classifications? If not, what is different about them? (Thanks
to Amanda Bauer)
Plate |
Fiber |
293/51994 |
185 |
293/51994 |
220 |
352/51789 |
242 |
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