We present the effective temperatures (Teff), metallicities, and colours in Sloan Digital Sky Survey (SDSS), Two Micron All Sky Survey, and Wide-field Infrared Survey Explorer filters, of a sample of 3834 late-K and early-M dwarfs selected from the SDSS Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectroscopic survey ASPCAP (APOGEE Stellar Parameters and Chemical Abundances Pipeline) catalogue. We confirm that ASPCAP Teff values between 3550 < Teff < 4200 K are accurate to ∼100 K compared to interferometric Teff values. In that same Teff range, ASPCAP metallicities are accurate to 0.18 dex between −1.0 <[M/H]<0.2. For these cool dwarfs, nearly every colour is sensitive to both Teff and metallicity. Notably, we find that g − r is not a good indicator of metallicity for near-solar metallicity early-M dwarfs. We confirm that J − KS colour is strongly dependent on metallicity, and find that W1 − W2 colour is a promising metallicity indicator. Comparison of the late-K and early-M dwarf colours, metallicities, and Teff to those from three different model grids shows reasonable agreement in r − z and J − KS colours, but poor agreement in u − g, g − r, and W1 − W2. Comparison of the metallicities of the KM dwarf sample to those from previous colour–metallicity relations reveals a lack of consensus in photometric metallicity indicators for late-K and early-M dwarfs. We also present empirical relations for Teff as a function of r − z colour combined with either [M/H] or W1 − W2 colour, and for [M/H] as a function of r − z and W1 − W2 colour. These relations yield Teff to ∼100 K and [M/H] to ∼0.18 dex precision with colours alone, for Teff in the range of 3550–4200 K and [M/H] in the range of −0.5–0.2
Monthly Notices of the Royal Astronomical Society
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This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016 Schmidt, et al. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Schmidt, Sarah J.; Wagoner, Erika L.; Johnson, Jennifer A.; Davenport, James R. A.; Stassun, Keivan G.; Souto, Diogo; and Ge, Jian, "Examining the Relationships Between Colour, Teff, and [M/H] for APOGEE K and M Dwarfs" (2016). Physics & Astronomy. 11.