PI: Saurav Dhital, Vanderbilt University, Saurav.Dhital@Vanderbilt.Edu
Address: Department of Physics & Astronomy, 6301 Stevenson Ctr Lane, Nashville, TN 37235, USA
CoI: Sebastien Lepine, American Museum of Natural History
CoI: Andrew A. West, Boston University
CoI: Keivan G. Stassun, Vanderbilt University
Title: Calibrating the Relative Metallicity Scale of M Subdwarfs Using Wide, Common Proper Motion Binaries
Abstract: Metallicity is an important parameter that determines all aspects of stellar evolution and observable properties but is very hard to measure for M dwarfs. M dwarf binaries provide coeval laboratories for studying the properties of the most numerous stellar constituents of the Milky Way; using their common metallicity, we can empirically determine how various molecular indices change with effective temperature. However, despite their ubiquity, M dwarfs are intrinsically faint; previous studies of resolved M dwarf binaries have been limited to small samples, which consist largely of disk dwarfs and are notoriously deficient in metal-poor systems. We propose to observe a sample of ~51 subdwarf (i.e. metal-poor dwarf) binaries to determine how the relative bandstrengths of CaH and TiO vary with metallicity and temperature in low-mass stars. By combining our proposed subdwarf binary sample with previously observed low-mass pairs, we will refine the CaH/TiO-based relative metallicity and probe a large range of metallicity and effective temperature. In addition, we will be able to confirm the binarity of these common proper motion halo pairs and study dynamical evolution/destruction of wide halo binaries. In combination with ongoing companion studies, this will pave the way towards a absolute metallicity scale for M dwarfs and a comprehensive study of chemical and dynamical evolution of the Galaxy.
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