0 Assigned ID: 242 ----- Attempting Submission 1 (Thu Apr 04 19:10:30 GMT 2019) ----- HST Phase I Proposal 242 (RGBTeff.apt) successfully submitted. Receipt: # 242-1 ----- Attempting Submission 2 (Fri Apr 05 13:39:56 GMT 2019) ----- State-of-the-art stellar evolution models contain systematic uncertainties in the effective temperature scale of the red giant branch (RGB) at the level of 100-200K (Tayar et al. 2017; Salaris et al. 2018; Choi et al. 2018). These uncertainties can be traced to two key effects in stellar interior and evolutionary models: the treatment of the outer (i.e., atmosphere) boundary condition coupled to the treatment of convection. These uncertainties are major, and in some cases dominant, sources of systematic errors in the modeling of resolved and unresolved stellar populations (e.g., Williams et al. 2017). Accurate models of RGB stars are essential for many areas in astrophysics including (1) estimating asteroseismic masses and ages of individual RGB stars in the Galaxy, (2) determining photometric metallicities and star formation histories from resolved stars in nearby galaxies, and 3) inferring ages, metallicities, and the dust content via the integrated light analysis of large samples of unresolved galaxies across cosmic time. The goal of this proposal is to produce new, high-fidelity stellar atmosphere and interior models of the RGB through a combination of technical innovations and rigorous calibration against high-quality stellar data in the Milky Way from HST and Gaia. This proposal is relevant to the Fundamental Physics initiative, specifically the focus on the tip of the RGB as a rung in the distance ladder. The results of this proposal will benefit all scientists engaged in the study of stellar populations using HST. Prof. Charlie Conroy has expertise in stellar populations research ranging from resolved stellar populations in the Milky Way to the interpretation of unresolved stellar populations in distant galaxies. Prof. Conroy is also an expert in the use of the ATLAS model atmosphere and SYNTHE spectral synthesis codes that feature prominently in this proposal. Dr. Aaron Dotter is an expert in stellar evolution modeling and the production of stellar isochrones. Dr. Dotter is a member of the development team for the Modules for Experiments in Stellar Astrophysics (MESA) stellar evolution code and maintainer of the MESA Isochrones and Stellar Tracks (MIST) stellar model library. Prof. Dan Weisz has expertise in the derivation of star formation histories of resolved stellar populations in Milky Way satellites, Local Group galaxies, and beyond. Stellar Physics Stellar Populations 0 Regular false true false true false SUPPORTED