A new and Homogeneous metallicity scale for Galactic classical Cepheids

Abstract

Context. 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. Aims. The main aim of this investigation is to perform a new and accurate abundance analysis of 20 calibrating Galactic Cepheids. We used high spectral resolution (R ~ 40 000–115 000) and high S/N spectra (~400), covering the entire pulsation cycle. Methods. We focused our attention on plausible systematics that would affect 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 that display abundance variations along the pulsation cycle. Results. The spectroscopic approach we developed brings forward small dispersions in the variation of the atmospheric parameters (σ(Teff) ~ 50 K, σ(log g) ~ 0.2 dex, and σ(ξ) ~ 0.2 kms−1) as well as in the abundance of both iron (≲0.05 dex) and α elements (≲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/Teff as a function of the pulsation phase. Conclusions. The current findings are a good viaticum for tracing the chemical enrichment of the Galactic thin disk by using classical Cepheids as a fundamental stepping stone for further investigations into the more metal-poor regime that is typical of Magellanic Cepheids.

An Improved Calibration of the Wavelength Dependence of Metallicity on the Cepheid Leavitt Law

“…Ideally, these new distance measurements will have to be combined with consistent metallicity estimates of all MW Cepheids obtained in a single system, spanning a wide range of abundances. In this sense, improvements are also expected from the use of recently published (Ripepi et al 2021;Romaniello et al 2022;da Silva et al 2022) and upcoming abundance catalogs for MW, LMC, and SMC Cepheids, which should again help to calibrate the metallicity effect with better accuracy.…”

High-resolution Spectroscopic Metallicities of Milky Way Cepheid Standards and Their Impact on the Leavitt Law and the Hubble Constant

“…High-resolution spectroscopic metallicities for several bright solar neighbourhood Cepheids are available in the literature that were primarily used to investigate the abundance gradient in the thin disk and/or the impact of metallicity on PL relations (e.g., Genovali et al 2014Genovali et al , 2015Luck 2018;Ripepi et al 2021;da Silva et al 2022;Kovtyukh et al 2022). Complementing metal-rich Cepheids in the solar vicinity, Trentin et al (2023) provided high-resolution spectra for the most metal-poor Galactic Cepheids that will be useful for an improved quantification of the metallicity dependence of PL relations.…”

The TYPHOON Stellar Population Synthesis Survey. I. The Young Stellar Population of the Great Barred Spiral NGC 1365

“…The situation in the center of NGC 1365 is not as unique as it seems. The Milky Way shows a metallicity of the young stellar population, which increases from [Z] ∼ −0.35 at 15 kpc galactocentric distance to ∼+0.3 at 4 kpc (Genovali et al 2014;da Silva et al 2022) but suddenly drops to solar or even subsolar toward the galactic center (Najarro et al 2004(Najarro et al , 2009Martins et al 2008;Davies et al 2009aDavies et al , 2009bOriglia et al 2013;Do et al 2015). Figure 5 in Genovali et al (2014) gives an excellent impression of the very similar situation in the Milky Way.…”