Absorption lines in the spectra of some binary stars are seen to change periodically from single to double lines and back again. Explain.
A) The effect of the gravitational field of one star on the atoms of the second star periodically produces spectral line shifts.
B) The magnetic field of one star produces Zeeman periodic splitting of spectral lines in atoms of the second star.
C) Oscillations on the surfaces of the stars lead to Doppler-shifted lines.
D) Motion toward and away from Earth during their orbital motion results in Doppler shift of light from these stars at times and no shift when the stars are moving perpendicular to the line of sight.

Question

Quizplus · Accepted Answer

The periodic change from single to double absorption lines in the spectra of some binary stars is due to their orbital motion. When the stars move toward or away from Earth, their light is Doppler shifted, leading to the appearance of double lines. When they move perpendicular to our line of sight, there is no Doppler shift, and the lines appear as single. This effect is not caused by gravitational, magnetic fields, or surface oscillations but by the relative motion of the stars with respect to the observer.

Absorption Lines in the Spectra of Some Binary Stars Are