Program: GS-2023A-Q-142

Title:TOWARDS A TRULY EMPIRICAL POPULATION II MASS-LUMINOSITY RELATIONSHIP
PI:Rene Mendez
Co-I(s): Marcelo Mora, Jennifer Anguita-Aguero

Abstract

We propose a continuation of multi-epoch Zorro Speckle observations of sub-solar metallicity binary systems, which will have a decisive impact on our current understanding about the role of metallicity on the mass-luminosity relation. All our targets are either known single- or double-line spectroscopic binaries. They have been recently scrutinized either with lower-precision Speckle observations with 4m telescopes, or with Zorro between 2019 and 2022. Several objects of our sample already have a few orbital points obtained with Gemini-S&N. Our full binary sample spans a large range of [Fe/H], down to -2.0. Gemini observations are needed to compute a high-precision resolved (visual) orbit (hence a system´s mass sum), as well as to obtain better-determined individual magnitudes and colors. Most of these systems have well-determined mass fractions from previous spectroscopy, so, when combined with our Gemini orbits and the exquisite Gaia parallaxes, high-precision individual component masses (and luminosities) will immediately follow. With the full data set, it will be possible to make a major contribution to the main-sequence mass-luminosity relation for metal-poor stars, and also to conduct sensitive tests of stellar evolutionary models for them. Furthermore, component colors and magnitudes for the lowest metallicity members in our sample, will place new points on the empirical Population II main sequence. This is important for the calibration of ages and distances to globular clusters, and therefore for understanding the early evolutionary phases of our Galaxy.