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We present a complete theoretical scenario for classical Cepheids in the mostcommonly used HST/WFC3 filters, going from optical (F555W, F606W and F814W) tonear-infrared (F160W) bands. The importance of such a study is related to therecent release of new classical Cepheids observed with HST/WFC3 in 8 distantgalaxies where SNIa are hosted. These observations have posed sound constraintsto the current distance scale with uncertainties on the Hubble constant Hosmaller than 3%. Our models explore a large range of metallicity and Heliumcontent, thus providing a robust and unique theoretical tool for describingthese new and future HST/WFC3 observations. As expected, the Period-Luminosity(PL) relation in F160W filter is linear and slightly dependent on themetallicity when compared with optical bands, thus it seems the most accuratetool to constrain extragalactic distances with Cepheids. We compare thepulsation properties of Cepheids observed with HST/WFC3-IR with our theoreticalscenario and we discuss the agreement with the predicted Instability Strip forall the investigated galaxy samples including the case of NGC4258. Finally,adopting our theoretical F160W PL relation for Z=0.02 and log P>1.0, we derivenew distance moduli. In particular, for NGC 4258, we derive a distance modulusmu0 = 29.345 +- 0.004 mag with a sigma = 0.34 mag, which is in very goodagreement with the geometrical maser value. Moreover, using the obtaineddistance moduli, we estimate the Hubble constant value, Ho=76.0 +- 1.9 km s-1Mpc-1 in excellent agreement with the most recent literature values.

Cepheid theoretical models and observations in HST/WFC3 filters: the effect on the Hubble constant Ho