Probing the Galactic halo with RR Lyrae stars - VI. The radial velocity curve templates of RRc stars

Abstract We present radial velocity (RV) curve templates of RRLyrae first-overtone stars (RRc) constructed with the MgI b triplet and Hα lines using time-domain medium-resolution survey spectra of 7 RRc stars from Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) Data Release 9. Furthermore, we derive the relation between the stellar RV curve amplitudes and g-band light curve amplitudes from Zwicky Transient Facility (ZTF) public survey. For those RRc stars without ZTF g-band light curves, we provide the conversions from the light curve amplitudes in ZTF r- and i-bands, Gaia G-band, and V-band from the All-Sky Automated Survey for upernovae (ASAS-SN) survey to the ones in ZTF g-band. We validate our RV curve templates using the RRc star SV Scl and find the uncertainties of systemic RV are less than 3.21 km s -1 and 6.43 km s -1 based on the MgI b triplet and Hα lines, respectively. We calculate the systemic RVs of 30 RRc stars using the RV curve templates constructed with the MgI b triplet and Hα lines and find the systemic RVs are highly consistent with each other. This RV curve template will be especially useful for obtaining the systemic RV of RRc using the LAMOST spectroscopy.