Double start - characteristic frequencies of the light

[mmfoley]

How can an astronomer recognize a double star from the characteristic frequencies of the light that reaches him from its member stars? I have looked and looked in my textbook but I cannot come up with the answer to this one.

Thank you!
mmfoley

 

[Adrian Baker]

Originally posted by mmfoley
How can an astronomer recognize a double star from the characteristic frequencies of the light that reaches him from its member stars? I have looked and looked in my textbook but I cannot come up with the answer to this one.

Thank you!
mmfoley

For a start, the motion of the two stars will shift their frequencies. If as we look from Earth, one is approaching us and the other moving away (as they orbit each other) then their frequencies will be blue and red shifted respectively.

By examining the spectral lines, the astronomer can see that some lines within it are blue shifted and some red. Those that are Red shifted belong to one star, those that are blue shifted belong to the other. This tells us that two stars are present.

 

[mmfoley]

thanks

Thank you for the reply and putting me on the right track.