0 Assigned ID: 694 ----- Attempting Submission 1 (Fri Mar 06 19:28:58 GMT 2020) ----- HST Phase I Proposal 694 successfully submitted. Receipt: # 694-1 ----- Attempting Submission 2 (Fri Mar 06 22:20:33 GMT 2020) ----- HST Phase I Proposal 694 successfully submitted. Receipt: # 694-2 ----- Attempting Submission 3 (Fri Mar 06 22:30:19 GMT 2020) ----- HST Phase I Proposal 694 successfully submitted. Receipt: # 694-3 ----- Attempting Submission 4 (Fri Mar 06 23:33:16 GMT 2020) ----- HST Phase I Proposal 694 successfully submitted. Receipt: # 694-4 ----- Attempting Submission 5 (Fri Mar 06 23:43:30 GMT 2020) ----- HST Phase I Proposal 694 successfully submitted. Receipt: # 694-5 ----- Attempting Submission 6 (Fri Mar 06 23:48:04 GMT 2020) ----- HST Phase I Proposal 694 successfully submitted. Receipt: # 694-6 ----- Attempting Submission 7 (Fri Mar 06 23:52:16 GMT 2020) ----- Upcoming high-resolution observing facilities will enable direct measurements of distances in the Hubble flow that are fully independent of other standard candles via the tip of the red giant branch (TRGB). These facilities (JWST, WFIRST, ELTs, and others) will perform optimally in the near-infrared, where the behavior of the TRGB remains unevenly characterized. To fully exploit future capabilities, we require a thorough characterization of the NIR TRGB with archival data. We propose to use archival F814W, F110W, and F160W observations of IC 1613, M31, and M33 to perform the first fully empirical, fully self-consistent calibration of the HST NIR-TRGB color-magnitude relation to date, including rigorous tests of potential systematics. Existing observations of M31 and M33 in particular provide unparalleled laboratories for performing this study, as they span a wide range of relevant characteristics such as ages, metallicities, surface densities, and dust geometries -- all of which can affect the NIR TRGB's measured luminosity in complex and subtle ways. This work will provide a necessary complement to current NIR-TRGB studies that focus on more distant targets, and will lay critical groundwork for the next generation of distance scale measurements. PI Durbin led a Cycle 25 archival proposal investigating the NIR-TRGB (AR-15016), the results of which are currently under review. In addition, they are a former member of the HST/WFC3 instrument team and are well-versed in WFC3-IR data analysis. Dr. Dalcanton has led the surveys of M31 and M33 that this proposal is based on (PHAT & GO-14610), and Dr. Williams is the architect of the photometry pipeline used for the PHAT high-level science products. Drs. Beaton and Seibert constructed the CCHP pipeline to which we will compare results, and have relevant expertise on both the TRGB specifically and the local distance ladder generally. Dr. McQuinn is leading a Cycle 27 program to study the NIR TRGB in several high-metallicity systems outside the Local Group (GO-15917). Stellar Populations and the Interstellar Medium Stellar Physics and Stellar Types 0 Regular false false false false false SUPPORTED