Absorption Lines in the Spectra of Some Binary Stars Are

Multiple Choice

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.