Stellar Characterization of M Dwarfs from the APOGEE Survey: A Calibrator Sample for M-dwarf Metallicities
Diogo Souto, Kátia Cunha, Verne V. Smith, Carlos Allende Prieto, Adam J. Burgasser, Kevin R. Covey, D. A. García–Hernández, Jon A. Holtzman, Jennifer A. Johnson, Henrik Jönsson, Suvrath Mahadevan, Steven R. Majewski, T. Masseron, Matthew Shetrone, Bárbara Rojas-Ayala, Jennifer Sobeck, Keivan G. Stassun, Ryan C. Terrien, Johanna Teske, Fábio Wanderley, O. Zamora
Abstract
Abstract We present spectroscopic determinations of the effective temperatures, surface gravities, and metallicities for 21 M dwarfs observed at high resolution ( R ∼ 22,500) in the H band as part of the Sloan Digital Sky Survey (SDSS)-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. The atmospheric parameters and metallicities are derived from spectral syntheses with 1D LTE plane-parallel MARCS models and the APOGEE atomic/molecular line list, together with up-to-date H 2 O and FeH molecular line lists. Our sample range in T eff from ∼3200 to 3800 K, where 11 stars are in binary systems with a warmer (FGK) primary, while the other 10 M dwarfs have interferometric radii in the literature. We define an <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>K</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>S</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> </mml:math> –radius calibration based on our M-dwarf radii derived from the detailed analysis of APOGEE spectra and Gaia DR2 distances, as well as a mass–radius relation using the spectroscopically derived surface gravities. A comparison of the derived radii with interferometric values from the literature finds that the spectroscopic radii are slightly offset toward smaller values, with Δ = −0.01 ± 0.02 R ⋆/ R ⊙ . In addition, the derived M-dwarf masses based upon the radii and surface gravities tend to be slightly smaller (by ∼5%–10%) than masses derived for M-dwarf members of eclipsing binary systems for a given stellar radius. The metallicities derived for the 11 M dwarfs in binary systems, compared to metallicities obtained for their hotter FGK main-sequence primary stars from the literature, show excellent agreement, with a mean difference of [Fe/H](M dwarf – FGK primary) = +0.04 ± 0.18 dex, confirming the APOGEE metallicity scale derived here for M dwarfs.