Insights into the Cepheid distance scale
G. Bono, F. Caputo, M. Marconi, I. Musella

TL;DR
This study investigates Cepheid variable stars to refine the Period-Luminosity relation, examining metallicity effects across different bands and validating theoretical models with observational data to improve distance measurements.
Contribution
It provides new empirical evidence on the metallicity dependence of Cepheid P-L relations and confirms theoretical predictions across multiple passbands.
Findings
The P-L slope steepens from optical to NIR bands.
Metallicity dependence of the slope decreases from B- to K-band.
Metallicity correction for P-WBV distances is -0.52 mag dex^-1.
Abstract
We present an investigation of Cepheid distances using theory and observations. Cepheid models indicate that the slope of the Period-Luminosity (P-L) relation covering the entire period range (0.40<= logP <=2.0) becomes steeper when moving from optical to NIR bands, and that the metallicity dependence of the slope decreases from the B- to the K-band. We estimated V- and I-band slopes for 87 Cepheid data sets belonging to 48 external galaxies with nebular oxygen abundance 7.5<= 12+log (O/H) <=8.9. By using Cepheid samples including more than 20 Cepheids, the chi^2 test indicates that the hypothesis of a steepening of the P-L_{V,I} relations with increased metallicity can be discarded at the 99% level. On the contrary, the observed slopes agree with the metallicity trend predicted by pulsation models, i.e. the slope is roughly constant for galaxies with 12+log (O/H) < 8.17 and becomes…
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