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A Volume-limited Sample of Ultracool Dwarfs. I. Construction, Space Density, and a Gap in the L/T Transition

Best, William M. J. ; Liu, Michael C. ; Magnier, Eugene A. ; Dupuy, Trent J.

The Astronomical journal, 2021-01, Vol.161 (1), p.42 [Periódico revisado por pares]

Madison: IOP Publishing

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  • Título:
    A Volume-limited Sample of Ultracool Dwarfs. I. Construction, Space Density, and a Gap in the L/T Transition
  • Autor: Best, William M. J. ; Liu, Michael C. ; Magnier, Eugene A. ; Dupuy, Trent J.
  • Assuntos: Astronomy ; Atmospheric evolution ; Atmospheric models ; Parallax ; Space density ; Statistical methods
  • É parte de: The Astronomical journal, 2021-01, Vol.161 (1), p.42
  • Descrição: Abstract We present a new volume-limited sample of L0–T8 dwarfs out to 25 pc defined entirely by parallaxes, using our recent measurements from UKIRT/WFCAM along with Gaia DR2 and literature parallaxes. With 369 members, our sample is the largest parallax-defined volume-limited sample of L and T dwarfs to date, yielding the most precise space densities for such objects. We find the local L0–T8 dwarf population includes young objects (≲200 Myr) and subdwarfs, as expected from recent studies favoring representative ages ≲4 Gyr for the ultracool field population. This is also the first volume-limited sample to comprehensively map the transition from L to T dwarfs (spectral types ≈L8–T4). After removing binaries, we identify a previously unrecognized, statistically significant (>4.4 σ ) gap ≈0.5 mag wide in colors in the L/T transition, i.e., a lack of such objects in our volume-limited sample, implying a rapid phase of atmospheric evolution. In contrast, the most successful models of the L/T transition to date—the “hybrid” models of Saumon & Marley—predict a pileup of objects at the same colors where we find a deficit, demonstrating the challenge of modeling the atmospheres of cooling brown dwarfs. Our sample illustrates the insights to come from even larger parallax-selected samples from the upcoming Legacy Survey of Space and Time by the Vera Rubin Obsevatory.
  • Editor: Madison: IOP Publishing
  • Idioma: Inglês
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