Metallicity calibration of metal-poor sub-dwarf M stars based on binary companions

Abstract

The low-mass stars are the most numerous stellar objects in the Galaxy with main sequence lifetimes that exceed the current age of the universe. Thus, they are great laboratories for studying the structure and evolution of the Galaxy. As the low-mass stars are becoming increasingly important sites to look for planets, the observational efficiency of such searches can be greatly enhanced with prior knowledge of stellar metallicity, since there are indications that M dwarf stars with known planets have sub-solar metallicities (eg. Bean et al. 2006). With the advent of large surveys like SDSS and 2MASS, the sample of photometric and spectroscopic data for low-mass dwarfs has increased significantly, with special emphasis on metal-poor sub-dwarf. The metallicities of these objects, along with their kinematic distributions, provide important constraints on the structure and composition of the halo of the Galaxy. This project will refine the calibration of metallicities of sub-dwarfs stars, poor in metals, which are in binary systems with large proper motions. The pairs consist of a sub-M dwarf and a star more massive (F or G, and sometimes K). As it is assumed that the binary share the same metallicity (originated from the same parent cloud), the composition of the most massive star (which can be accurately obtained via theoretical models) can be applied to sub-dwarf companion M. Some studies have used optical spectroscopy and infrared to bind spectroscopic characteristics to a range of metallicities (eg, Bean et al. 2006; Woolf et al. 2009; Rojas-Ayala et al. 2010). This work already has some observations from MDM and KPNO observatories that can already be used for analysis. The sample must be increased with requests for additional time at SOAR with Goodman spectrograph. The stars F/G pairs that constitute the stars sdM can have their metallicities estimated from correlations based on the strengths of CaH and TiO bands. It is expected that the kinematic analysis of the observed objects and is made during the doctoral candidate. (AU)