PHATTER M33 Cepheids HST phot. & distances

Using high-quality ground-based light curves, we recover Cepheid phases and amplitudes for multi-epoch HST data and we perform template fitting to derive intensity-averaged mean magnitudes. HST observations in the SH0ES near-infrared Wesenheit system significantly reduce the effect of crowding relative to ground-based data, as seen in the final PL scatter of {sigma}=0.11mag.

We adopt the absolute calibration of the PL based on HST observations in the Large Magellanic Cloud and a distance derived using late-type detached eclipsing binaries to obtain a distance modulus for M33 of {mu}=24.622+/-0.030mag (d=840+/-11kpc), a best-to-date precision of 1.3%. We find very good agreement with past Cepheid-based measurements. Several tip of the red giant branch estimates bracket our result while disagreeing with each other.