The radial-velocity curve of a star in a binary star system is a plot against time ofA) the speed of the star in a direction perpendicular to the line of sight to the star.B) the position of the star in celestial coordinates.C) the variation of Doppler shift of its spectral lines and hence of its speed toward or away from us.D) the temperature of the star as determined from the movement of the peak wavelength of its spectrum.
