An astronomer looks through a telescope and identifies a source that appears visually to be a single star. However, the source is later determined to be a binary system looking at its spectrum. Which of these spectral features would NOT characterize it as a binary?
A) The spectrum includes spectral lines associated with two different spectral types.
B) The sets of spectral lines move periodically to slightly higher frequencies and then slightly lower frequencies.
C) As the lines from one spectral type are moving toward higher frequencies, the lines from the other spectral type are moving toward lower frequencies.
D) The spectral lines from one spectral type become periodically brighter while the lines from the other spectral type become dimmer.

Question

Quizplus · Accepted Answer

The periodic brightening and dimming of spectral lines from different spectral types is not a characteristic used to identify binary star systems. Instead, binary systems are identified by the presence of spectral lines from two different stars (A), the Doppler shift causing these lines to move periodically to higher and lower frequencies (B), and the reciprocal motion of these lines as the stars orbit their common center of mass (C).

An Astronomer Looks Through a Telescope and Identifies a Source