Stellar Parameters for Trappist-1

Valérie Van Grootel, Catarina S. Fernandes, Michael Gillon, Emmanuel Jehin, Jean Manfroid, Richard Scuflaire, Adam J. Burgasser, Khalid Barkaoui, Zouhair Benkhaldoun, Artem Burdanov, Laetitia Delrez, Brice Olivier Demory, Julien De Wit, Didier Queloz, Amaury H.M.J. Triaud

Research output: Contribution to journalArticlepeer-review

45 Citations (Scopus)
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TRAPPIST-1 is an ultracool dwarf star transited by seven Earth-sized planets, for which thorough characterization of atmospheric properties, surface conditions encompassing habitability, and internal compositions is possible with current and next-generation telescopes. Accurate modeling of the star is essential to achieve this goal. We aim to obtain updated stellar parameters for TRAPPIST-1 based on new measurements and evolutionary models, compared to those used in discovery studies. We present a new measurement for the parallax of TRAPPIST-1, 82.4± 0.8 mas, based on 188 epochs of observations with the TRAPPIST and Liverpool Telescopes from 2013 to 2016. This revised parallax yields an updated luminosity of L∗= (5.22 ±0.19)×10-4 L⊙, which is very close to the previous estimate but almost two times more precise. We next present an updated estimate for TRAPPIST-1 stellar mass, based on two approaches: mass from stellar evolution modeling, and empirical mass derived from dynamical masses of equivalently classified ultracool dwarfs in astrometric binaries. We combine them using a Monte-Carlo approach to derive a semi-empirical estimate for the mass of TRAPPIST-1. We also derive estimate for the radius by combining this mass with stellar density inferred from transits, as well as an estimate for the effective temperature from our revised luminosity and radius. Our final results are M∗ = 0.089 ± 0.006 M⊙, R∗ = 0.121 ± 0.003 R⊙, and Teff = 2516± 41 K. Considering the degree to which the TRAPPIST-1 system will be scrutinized in coming years, these revised and more precise stellar parameters should be considered when assessing the properties of TRAPPIST-1 planets.

Original languageEnglish
Article number30
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 19 Jan 2018


  • stars: individual (TRAPPIST-1)
  • stars: late-type
  • stars: low-mass

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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