http://arxiv.org/abs/1911.04612
Large numbers of low-to-medium resolution spectra of M-type dwarf stars from both the local Galactic disk and halo are available from various surveys. In order to fully exploit these data, we develop a template-fit method using a set of empirically assembled M dwarf/subdwarf classification templates, based on the measurements of the TiO and CaH molecular bands, to classify M dwarfs/subdwarfs by spectral type and metallicity class. We further present a pipeline to automatically determine the effective temperature, metallicity ([M/H]), alpha-element to iron abundance ratio ([alpha/Fe]), and surface gravity of M dwarfs/subdwarfs using the latest version of BT-Settl model atmospheres. We apply these methods to a set of low-to-medium resolution optical spectra of 1,544 high proper-motion (> 0.4″/yr) M dwarfs/subdwarfs. Our metallicity estimates appear to be consistent with the expected color-magnitude variation of stars relative to atmospheric composition, as our sample shows a clear stratification with respect to metallicity in the Gaia H-R diagram. Furthermore, the measured chemical parameters of the two components in 48 binary systems are in a good agreement with each other, which suggest a precision of 0.22 dex in [M/H], 0.08 dex in [alpha/Fe], and 0.16 dex in the combined index [alpha/Fe]+[M/H]. There is also a good consistency between metallicity class, obtained from the empirical classification templates, and the index [alpha/Fe]+[M/H] (~ [alpha/H]), obtained from model-fitting, which means that the more easily measured metallicity class can be used as a relatively reliable indicator of absolute alpha-element abundance, [alpha/H], in low-mass stars. Finally, we examine the distribution of our stars in the [alpha/Fe] vs. [M/H] diagram, which shows evidence of clustering in chemical abundance makeup, suggestive of discrete populations among the local disk and halo stars.
N. Hejazi, S. Lepine, D. Homeier, et. al.
Wed, 13 Nov 19
53/73
Comments: 53 pages, 43 figures, 10 tables, accepted for publication in AJ
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