In a spectroscopic binary, if a pair shows a combined set of lines tonight, but a maximum split two nights later, what must its orbital period be?
1 Answer
Jun 4, 2016
Eight days.
Explanation:
Think of the splitting of the lines as two sine waves. They are 180 degrees out of phase because when Star A moves toward Earth making a blue shift, the Star B is moving away from Earth making a red shift.
Intial state: spectral lines together.
1/4 period: Star A reached its maximum blue shift (think of it as a peak in the sine wave), Star B reaches its maximum red shift (trough).
1/2 period: Spectral lines are back together.
3/4 period: Star A has a maximum red shift (trough), Star B a maximum blue shift (crest). Reverse of 1/4 period.
Full period: Back to the initial state for another cycle.
