F. Thévénin | Searcharxiv

arXiv2026

On the use of field RR Lyrae as Galactic probes:. IX. Radial velocities

We present the largest and most homogeneous catalog of radial velocity (RV) measurements for field RR Lyrae (RRL) variables, based on both proprietary and publicly available spectroscopic data. The sample includes 17,563 RRLs pulsating in the fundamental mode (12,353 RRab), in the first overtone (5,011 RRc), and in double-mode (199 RRd). The RV curve (RVC) templates for metallic and Balmer lines were used to derive RV amplitudes and $V_γ$ velocities, defined as the RV of the stellar barycenter with respect to the Sun. The typical accuracy across the catalog is on average 3.8 km s$^{-1}$ for well-sampled RVCs, 6.5 km s$^{-1}$ for RVCs with 3-7 phase points and 11.3 km s$^{-1}$ for RVCs with fewer than three phase points. The use of different spectroscopic diagnostics and RVC templates provides, within the errors, very similar $V_γ$ velocities. We found that the metallicity dependence of RV amplitudes is vanishing for metallic lines, but becomes increasingly significant for H$γ$ and H$δ$. Moreover, the scaling relations between photometric (V, $G_{BP}$, G, $G_{RP}$) and RV amplitudes are linear for RRc and nonlinear for RRab variables, independently of the adopted diagnostic. This circumstantial evidence indicates that convection affects more luminosity than RV amplitudes when moving from the blue (hot) to the red (cool) edge of the instability strip. The spectroscopic Bailey diagram (RV amplitude versus period) shows a smooth transition and a reduced spread at a fixed period, when moving from metal-poor to metal-rich RRLs. Finally, we also found evidence that the metallicity distribution function of Blazhko RRLs is skewed toward the metal-intermediate and metal-rich regimes.

astro-ph.SR↗

arXiv2022

A new and homogeneous metallicity scale for Galactic classical Cepheids II. The abundance of iron and alpha elements

Classical Cepheids are the most popular distance indicators and tracers of young stellar populations. The key advantage is that they are bright and they can be easily identified in Local Group and Local Volume galaxies. Their evolutionary and pulsation properties depend on their chemical abundances. The main aim of this investigation is to perform a new and accurate abundance analysis of two tens of calibrating Galactic Cepheids using high spectral resolution (R$\sim$40,000-115,000) and high S/N spectra ($\sim$400) covering the entire pulsation cycle. We focus our attention on possible systematics affecting the estimate of atmospheric parameters and elemental abundances along the pulsation cycle. We cleaned the line list by using atomic transition parameters based on laboratory measurements and by removing lines that are either blended or display abundance variations along the pulsation cycle. The spectroscopic approach that we developed brings forward small dispersions in the variation of the atmospheric parameters ($σ$($T_{\rm eff}$)$\sim$50 K, $σ$($\log{g}$)$\sim$0.2 dex, and $σ$($ξ$)$\sim$0.2 km/s) and in the abundance of both iron ($\lesssim$ 0.05 dex) and alpha elements ($\lesssim$0.10 dex) over the entire pulsation cycle. We also provide new and accurate effective temperature templates by splitting the calibrating Cepheids into four different period bins, ranging from short to long periods. For each period bin, we performed an analytical fit with Fourier series providing $θ= 5040/{T_{\rm eff}}$ as a function of the pulsation phase. The current findings are a good viaticum to trace the chemical enrichment of the Galactic thin disk by using classical Cepheids and a fundamental stepping stone for further investigations into the more metal-poor regime typical of Magellanic Cepheids.

astro-ph.SR↗