not take the pulsation into account, but we assume the validity of the quasi-static approximation for the Cepheid atmosphere [see, e.g., @Molinaro-2011]. Line lists were extracted from the Vienna Atomic Line Database (VALD). Although these lists differ from the original list provided by Kurucz, the redshift estimates were essentially unaffected (the following results in our paper would remain unchanged within $1~{{\mathrm{km~s}^{-1}}}$). Figure \[fig:comp\] illustrates the method used to measure the redshifts; a telluric absorption spectrum constructed from an A-type star observation (1) was convolved with a model spectrum shifted by a trial redshift (2) to construct a synthesized spectrum (3). The synthetic spectrum was then compared with the observed spectrum (4). Each target spectrum was assigned the redshift that minimized the $\chi ^2$ value of the difference between (3) and (4); the residual obtained by subtracting (3) from (4) is indicated in the lower panel of Figure \[fig:comp\]. The reduced $\chi^2$ value is typically $\sim 25$. Although some differences exist among the spectra of the four Cepheids and between the model and observed spectra, such differences were annulled by the many common absorption lines, thus exerting negligible effects on the radial velocity measurements. Therefore, for every spectrum, we applied the 