On the Use of Field RR Lyrae as Galactic Probes. V. Optical and radial
  velocity curve templates
  We collected the largest spectroscopic catalog of RR Lyrae (RRLs) including
$\approx$20,000 high-, medium- and low-resolution spectra for $\approx$10,000
RRLs. We provide the analytical forms of radial velocity curve (RVC) templates.
These were built using 36 RRLs (31 fundamental -- split into three period bins
-- and 5 first overtone pulsators) with well-sampled RVCs based on three groups
of metallic lines (Fe, Mg, Na) and four Balmer lines (H$_\alpha$, H$_\beta$,
H$_\gamma$, H$_\delta$).
  We tackled the long-standing problem of the reference epoch to anchor light
curve and RVC templates. For the $V$-band, we found that the residuals of the
templates anchored to the phase of the mean magnitude along the rising branch
are $\sim$35\% to $\sim$45\% smaller than those anchored to the phase of
maximum light. For the RVC, we used two independent reference epochs for
metallic and Balmer lines and we verified that the residuals of the RVC
templates anchored to the phase of mean RV are from 30\% (metallic lines) up to
45\% (Balmer lines) smaller than those anchored to the phase of minimum RV.
  We validated our RVC templates by using both the single- and the three-phase
points approach. We found that barycentric velocities based on our RVC
templates are two-three times more accurate than those available in the
literature. We applied the current RVC templates to Balmer lines RVs of RRLs in
the globular NGC~3201 collected with MUSE at VLT. We found the cluster
barycentric RV of $V_{\gamma}$=496.89$\pm$8.37(error)$\pm$3.43 (standard
deviation) km/s, which agrees well with literature estimates.
