Insights into the Cepheid distance scale

Understand

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.