Stellar and Planetary Characterization of the Ross 128 Exoplanetary System from APOGEE Spectra

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The first detailed chemical abundance analysis of the M-dwarf (M4.0) exoplanet-hosting star Ross 128 is presented here, based upon near-infrared (1.5-1.7 μm), high-resolution (R ∼ 22,500) spectra from the SDSS Apache Point Galactic Evolution Experiment survey. We determined precise atmospheric parameters T eff = 3231 ±100 K, log g = 4.96 ±0.11 dex and chemical abundances of eight elements (C, O, Mg, Al, K, Ca, Ti, and Fe), finding Ross 128 to have near solar metallicity ([Fe/H] = +0.03 ± 0.09 dex). The derived results were obtained via spectral synthesis (1D LTE) adopting both MARCS and PHOENIX model atmospheres; stellar parameters and chemical abundances derived from the different adopted models do not show significant offsets. Mass-radius modeling of Ross 128b indicates that it lies below the pure-rock composition curve, suggesting that it contains a mixture of rock and iron, with the relative amounts of each set by the ratio of Fe/Mg. If Ross 128b formed with a subsolar Si abundance, and assuming the planet's composition matches that of the host star, it likely has a larger core size relative to the Earth despite this producing a planet with a Si/Mg abundance ratio ∼34% greater than the Sun. The derived planetary parameters - insolation flux (S Earth = 1.79 ±0.26) and equilibrium temperature (T eq = 294 ±10 K) - support previous findings that Ross 128b is a temperate exoplanet in the inner edge of the habitable zone.


  • Diogo Souto
  • Cayman T. Unterborn
  • Verne V. Smith
  • Katia Cunha
  • Johanna Teske
  • Kevin Covey
  • Bárbara Rojas-Ayala
  • D. A. García-Hernández
  • Keivan Stassun
  • Olga Zamora
  • Thomas Masseron
  • J. A. Johnson
  • Steven R. Majewski
  • Henrik Jönsson
  • Steven Gilhool
  • Cullen Blake
  • Felipe Santana
Enheter & grupper
Externa organisationer
  • National Observatory Brazil
  • Arizona State University
  • University of Arizona
  • Carnegie Institution for Science
  • Carnegie Observatories
  • Western Washington University
  • Andrés Bello National University
  • Instituto de Astrofísica de Canarias
  • University of La Laguna (ULL)
  • Ohio State University
  • University of Virginia
  • University of Pennsylvania
  • University of Chile
  • National Optical Astronomy Observatory
  • Vanderbilt University
  • Fisk University

Ämnesklassifikation (UKÄ) – OBLIGATORISK

  • Astronomi, astrofysik och kosmologi


TidskriftAstrophysical Journal Letters
Utgåva nummer1
StatusPublished - 2018 jun 10
Peer review utfördJa