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The radio velocity convention

Starting from Eq. 4, we obtain to first order in $\ensuremath{v_{\ensuremath{\mathrm{\parallel}}}^{\ensuremath{\mathrm{obs}}}}/\ensuremath{c}$

\begin{displaymath}
\ensuremath{f_\ensuremath{\mathrm{}}^{\ensuremath{\mathrm{o...
...el}}}^{\ensuremath{\mathrm{obs}}}}}{\ensuremath{c}} \right) }.
\end{displaymath} (6)

In this case, we can establish a linear velocity scale (see Sect. 1.3.2)
\begin{displaymath}
\ensuremath{v_{\ensuremath{\mathrm{}}}^{\ensuremath{\mathrm...
...{f_\ensuremath{\mathrm{tuned}}^{\ensuremath{\mathrm{rest}}}}}.
\end{displaymath} (7)

This linear velocity scale is only a first order approximation, which is called the radio velocity convention. Indeed, it is well adapted to the radio spectrometer because 1) their natural output is a spectral axis regularly spaced in frequency and 2) the radio velocity convention gives a linear relation between the velocity and the frequency scale. This is why this convention is the default in CLASS.



Gildas manager 2015-03-01