PROSPECTING IN ULTRACOOL DWARFS: MEASURING THE METALLICITIES OF MID- AND 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 dwarf atmospheres make it difficult to measure their metallicities using techniques that have been commonly used for Sun-like stars. Although the...

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Bibliographic Details
Published in:The Astronomical journal 2014-06, Vol.147 (6), p.1-11
Main Authors: Mann, Andrew W, Deacon, Niall R, Gaidos, Eric, Ansdell, Megan, Brewer, John M, Liu, Michael C, Magnier, Eugene A, Aller, Kimberly M
Format: Article
Language:English
Subjects:
ABUNDANCE
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Asymptotic properties
ATMOSPHERES
BINARY STARS
CALIBRATION
DWARF STARS
Iron
IRON 58
METALLICITY
MOLECULES
Prospecting
RESOLUTION
SPECTRA
Stars
SUN
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Summary:Metallicity is a fundamental parameter that contributes to the physical characteristics of a star. The low temperatures and complex molecules present in M dwarf atmospheres make it difficult to measure their metallicities using techniques that have been commonly used for Sun-like stars. Although there has been significant progress in developing empirical methods to measure M dwarf metallicities over the last few years, these techniques have been developed primarily for 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 ([Asymptotically = to]2.2 mu m) 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 accurate to ~0.07 dex 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 show that our method gives consistent metallicities for the components of M+M wide binaries. We verify that our new formula works for unresolved binaries by combining spectra of single stars. Lastly, we show that our calibration gives consistent metallicities with the Mann et al. study for overlapping (M4-M5) stars, establishing that the two calibrations can be used in combination to determine metallicities across the entire M dwarf sequence.
ISSN:0004-6256
1538-3881
1538-3881
DOI:10.1088/0004-6256/147/6/160