M-Subdwarfs: Spectroscopic Classification and the Metallicity Scale

1 February 1997

journal article
Published by American Astronomical Society in The Astronomical Journal

Vol. 113, 806-822
https://doi.org/10.1086/118302

Abstract

We present a spectroscopic classification system for M-dwarfs and M-subdwarfs based on quantitative measures of TiO and CaH features in the region 6200 - 7400 Angstroms. Our sample of cool stars covers the range from solar metallicity stars to the most extreme subdwarfs known. Using synthetic spectra computed by Allard and Hauschildt (1995), we derive metallicities for the stars. Stars are classified as dwarfs (M V), subdwarfs (sdM), or extreme subdwarfs (esdM). These classifications correspond to [m/H] ~ 0.0, -1.2, and -2.0 respectively. Our metallicity scale agrees with theoretical HR diagrams and HST globular cluster measurements. We discuss some nearby subdwarfs of particular interest in light of our metallicity scale.Comment: AASTeX, 43 pages, 11 figures, A.J. accepte

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