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 approximate to 20,000 high-, medium-, and low-resolution spectra for approximate to 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 five 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 similar to 35% to similar to 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-point and the three phase point approaches. We found that barycentric velocities based on our RVC templates are two to 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 +/- 8.37(error) +/- 3.43 (standard deviation) km s(-1), which agrees well with literature estimates.

Automated summary

The research team compiled a large amount of RR Lyrae spectroscopic data, provided the analytical forms of radial velocity curve templates, and solved the problem of reference epochs and light curve templates.