The RRC Stars: Chemical Abundances and Envelope Kinematics

TL;DR

This study provides detailed chemical abundance and kinematic analyses of RRc stars, comparing their properties with RRab stars, and investigates the Blazhko effect to challenge existing hypotheses.

Contribution

It introduces improved spectral co-addition methods, constructs radial velocity templates, and compares atmospheric structures of RRc and RRab stars, also testing the Blazhko hypothesis.

Findings

Spectral co-addition yields superior abundance results.

RRc abundances align with RRab stars' metallicities.

Radial velocity templates facilitate surveys.

Abstract

We analyzed series of spectra obtained for twelve stable RRc stars observed with the echelle spectro- graph of the du Pont telescope at Las Campanas Observatory and we analyzed the spectra of RRc Blazhko stars discussed by Govea et al. (2014). We derived model atmosphere parameters, [Fe/H] metallicities, and [X/Fe] abundance ratios for 12 species of 9 elements. We co-added all spectra ob- tained during the pulsation cycles to increase S/N and demonstrate that these spectra give results superior to those obtained by co-addition in small phase intervals. The RRc abundances are in good agreement with those derived for the RRab stars of Chadid et al. (2017). We used radial velocity measurements of metal lines and H{\alpha} to construct variations of velocity with phase, and center-of-mass velocities. We used these to construct radial-velocity templates for use in low-medium resolution radial velocity surveys of RRc stars. Additionally, we calculated primary accelerations, radius variations, metal and H{\alpha} velocity amplitudes, which we display as regressions against primary acceleration. We employ these results to compare the atmosphere structures of metal-poor RRc stars with their RRab counterparts. Finally, we use the radial velocity data for our Blazhko stars and the Blazhko periods of Szczygie l & Fabrycky (2007) to falsify the Blazhko oblique rotator hypothesis.