0 Assigned ID: 2314 ----- Attempting Submission 1 (Fri Apr 09 21:55:04 GMT 2021) ----- The Cepheid distance scale is at the center of a controversy concerning the expansion history of the Universe. If it is to become the basis for asserting the existence of new physics, every effort must be made to fully understand the data and its calibration and application. Our program will independently reduce and optimize the resolution on all of the HST Cepheid data calibrating SNe Ia used to reach the pure Hubble flow. We need to understand at what stage in the analysis the scatter in the period-luminosity relations grows from 0.1 to 0.4 mag. in parallel with the re-reduction, we will run two experiments targetting the systematic errors in every galaxy. One experiment will target "Sky Subtraction Bias", and can can be rapidly performed. The second will generate a grid of artificial stars, from which any Cepheid light curve can be built and the systematics quantified. This will explore "Amplitude Bias" in the Cepheid discovery, and "Sigma-Clipping Bias" in the production of PL relations. The Sky Bias in the first experiment will also be cross-checked in these more realistic, but significantly more CPU-intensive studies. New variability and period finding techniques will be introduced and applied. Techniques for proactively optimising future programs aimed at high-precision and high accuracy Cepheid distances will be emphasized. New observations with HST and JWST will be suggested for retroactively maximizing the precision of previously observed extragalactic Cepheid PL relations.his program will yield the most detailed estimation of the systematic errors on the Cepheid-based Ho to date. All CMD data and all detected variable stars will be made public. The PI, Kayla Owens is a graduate students in the Department of Astronomy & Astrophysics at the University of Chicago. She has experience in reducing ACS and WFC3 data and analysing-crowded field stellar photometry. This program will form the basis of her doctoral thesis. Dr. Barry F. Madore (Carnegie Observatories) has a long-standing interest and applied expertise in determining the expansion rate of the Universe, having pioneered the use of Cepheid variables and the TRGB Method, in the optical and in the near infrared. He was a founding member of the original HST Key Project on the Hubble constant and has over 100 refereed papers on this topic. Madore is a Visiting Professor at the University of Chicago and is in daily contact with Ms Owens concerning her ongoing research Stellar Physics and Stellar Types 0 Regular false false false false false SUPPORTED