@ACuriousMind On Wikipedia (
en.wikipedia.org/wiki/Doppler_effect), $c$ is not the speed of light but in the paper it is, so using $n=c/v_m$, where $v_m$ is the light speed in the medium, one ends up with the fraction $v/v_m$ in the numerator. And on Wikipedia, $c=v_m$ (it says "propagation speed of waves"...is there a difference between light and sound waves in this case?), so I get $\frac{1-v/v_m}{1+v/v_s}$ where $v_s$ is the speed of the source, and in the paper apparently $v_s=v$...