based on their 4-epoch spectroscopic observations using CRIRES at VLT. If this is true for our target Cepheids with $A_{H}\sim 0.4$ mag, we should consider the velocity amplitude $70~{{\mathrm{km~s}^{-1}}}$ rather than $55~{{\mathrm{km~s}^{-1}}}$. The difference, if any, between the velocity curves from optical, $H$- and $K$-band absorption lines is not established. Unfortunately, our spectroscopic observations are too few to determine the amplitudes. Thin curves in Figure \[fig:phase\_cor\] indicate fits obtained by assuming the larger amplitude ratio. Two horizontal lines in each panel indicate how the estimated mean velocity is affected by the amplitude ratio. The effect is small in the case of GCC-a which have two measurements around the mean, and the three points slightly prefer the predicted curve with the smaller amplitude ratio. The mean velocities of the others get offset by $\sim 7~{{\mathrm{km~s}^{-1}}}$. Velocity curves of Cepheids obtained with infrared spectra and their difference from those obtained with optical spectra should be investigated with more data as @Nardetto-2011 also suggested. We here adopt the results with the smaller amplitude ratio and they are listed in Table \[tab:vel\]. Considering the above uncertainties, the velocity amplitudes are expected be between $\sim 45~{{\mathrm{km~s}^{-1}}}$ and $\sim 80~{{\mathrm{km~s}^{-1}}}$ for a Cepheid with $A_{H}=0.4$ mag. 