Ok, I would suggest removing the word in front of the equations in the 3 docstrings. In addition, you need to end the first line (after velocity) with a . due to the way the API docs work (try building the docs and look at the API table and you'll see what I mean). So maybe something like:
 
```
Return the equivalency pairs for the optical convention for the Doppler shift.

The optical convention for the relation between velocity and frequency is:

:math:`V = c \frac{f_0 - f}{f  }  ;  f(V) = f_0 ( 1 + V/c )^{-1}

etc.
```

and same for the two other docstrings.