Another interesting phenomenon sometimes seen in SDSS data is that of a multiple star system. Sometimes the “star” spectrum you see actually comes from two or more stars orbiting each other. You may notice some spectra with two or more peak wavelengths, indicating two or more temperatures. These peaks could be due to the fact that you are actually looking at a multiple star system, and the stars have different temperatures. You may find a white dwarf orbiting a type G or K star, for example. You always need to keep in mind that any star you see may actually be a multiple star system.
The image below shows the spectrum of a double star system – notice the two peaks in the thermal radiation curve. Astronomers estimate that about half the stars in the sky are part of multiple star systems; however, if the smaller “companion star” is very faint and close to the larger star, you may not detect its spectrum.
To learn more about this star, see its entry in the Explore tool. Can you see both stars in the image?
Now, you are ready to use spectral types to conduct actual research projects in astronomy. Here are a few of possible follow up projects. Try one of these projects, or think of another question you would like to answer by classifying stars into spectral types.