Poster Abstracts

Name/Affiliation:  Andrew Mann (University of Texas at Austin)

Title:  Prospecting in Ultracool Dwarfs: Measuring the Metallicities of Mid- to Late-M Dwarfs

Metallicity is a fundamental parameter that contributes to the physical characteristics of a star. The low temperatures and complex molecules present in M dwarfs make it difficult to measure their metallicities using techniques that have been applied to Sun-like stars. Although there has been significant progress developing empirical methods to measure M dwarf metallicities over the last few years, these techniques have been developed to only work on early- to mid-M dwarfs. We present a method to measure the metallicity of mid- to late-M dwarfs from moderate resolution (R~2000) K-band (~2.2 micron) spectra. We calibrate our formula using 44 wide binaries containing an F, G, K, or early M primary of known metallicity and a mid- to late-M dwarf companion. We show that similar features and techniques used for early M dwarfs are still effective for late-M dwarfs. Our revised calibration is reliable for M4.5-M9.5 dwarfs with -0.58<[Fe/H]<+0.56 and shows no systematic trends with spectral type, metallicity, or the method used to determine the primary star metallicity. We verify that our new formula works for unresolved binaries by combining spectra of single stars and that it gives consistent metallicities for components of M+M wide binaries. Lastly, we show that our calibration gives consistent metallicities with the Mann et al. (2013a) study for overlapping (M4-M5) stars, indicating that the two calibrations can be used in unison to determine metallicities across the entire M dwarf sequence.