Examining the relationships between colour, $T_{\rm eff}$ , and [M/H] for APOGGE K and M dwarfs

Sarah J. Schmidt, Erika L. Wagoner, Jennifer A. Johnson, et al

ads:2016MNRAS.460.2611S

Published: May 13, 2016

Published in: MNRAS

Abstract:

We present the effective temperatures ( $T_{\rm eff}$ ), metallicities, and colours in SDSS, 2MASS, and WISE filters, of a sample of 3834 late-K and early-M dwarfs selected from the Sloan Digital Sky Survey APOGEE spectroscopic survey ASPCAP catalog. We confirm that ASPCAP $T_{\rm eff}$ values between 3550 K $<T_{\rm eff}<$ 4200 K are accurate to $\sim$ 100 K compared to interferometric $T_{\rm eff}$ values. In that same $T_{\rm eff}$ 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 $T_{\rm eff}$ 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 $J-K_S$ 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 $T_{\rm eff}$ to those from three different model grids shows reasonable agreement in $r-z$ and $J-K_S$ 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 $T_{\rm eff}$ 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 $T_{\rm eff}$ to $\sim$ 100 K and [M/H] to $\sim$ 0.18 dex precision with colours alone, for $T_{\rm eff}$ in the range of 3550–4200 K and [M/H] in the range of $-$ 0.5–0.2.

Summary

This is an exploration of the relation between color, temperature, and metallity for low mass stars in the Sloan Digital Sky Survey (SDSS), the Two Micron All-Sky Survey (2MASS), and the Wide-field Infrared Survey Explorer (WISE). The colors, temperatures, and metallicities for K and M dwarfs with accurate infrared spectra are compared with isochrone model grids and color-metallicity relations. This can be used as a way to estimate the temperatures and metallicities in a large sample of such stars with colors but noisy spectra. These estimates can then be used in constructing a metallicity distribution function for low mass stars.

Contribution

This is primarily a continuation of my undergraduate thesis project with a much larger data set and more isochrones tested.

Recommended Citation

Sarah J. Schmidt et al. 2016, MNRAS 460, 2611

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