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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.
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.