Chemical Properties of the Local Disk and Halo. II. Abundances of 3745 M Dwarfs and Subdwarfs from Improved Model Fitting of Low-resolution Spectra

Abstract

We present a model-fit pipeline to determine the stellar parameters of M-type dwarfs, which is an improvement on our previous work described in Hejazi et al. We apply this pipeline to analyze the low-resolution ( R ∼ 2000) spectra of 3745 M dwarfs/subdwarfs, collected at the MDM Observatory, Lick Observatory, Kitt Peak National Observatory, and Cerro Tololo Inter-American Observatory. We examine the variation of the inferred parameter values in the H-R diagram constructed from their Gaia Early Data Release 3 (EDR3) parallaxes and optical magnitudes. We also study the distribution of our stars in the abundance diagram of [ α /Fe] versus [M/H] and inspect the variation of their metallicity class, effective temperature, and surface gravity, as well as their Galactic velocity components U , V , and W , in this diagram. In addition, the analyses of the stars’ projected motions in the two-dimensional UV , VW , and UW planes, the variation of their chemical parameters in these planes, and their distribution in the abundance−velocity diagrams are important parts of this study. The precision of our model-fit pipeline is confirmed by the clear stratification of effective temperature and chemical parameters in the H-R diagram; the similarity of the stars’ distribution in the [ α /Fe] versus [M/H] diagram and in the metallicity−velocity planes to those from other studies; the revealing of substructure in the abundance−velocity diagrams; and chemical homogeneity between the components of a set of binary systems.