A Double-Line Spectroscopic Binary

A Double-Line Spectroscopic Binary
The spectrum of the double-line spectroscopic binary κ (kappa) Arietis has spectral lines that shift back and forth as the two
stars revolve around each other. (a) The stars are moving parallel to the line of sight, with one star approaching Earth,
the other star receding, as in Stage 1 or 3 of Figure 11-15. These motions produce two sets of shifted spectral lines. (b) Both stars
are moving perpendicular to our line of sight, as in Stage 2 or 4 of Figure 11-15. As a result, the spectral lines of the two stars
have merge