New evidence for a substellar luminosity problem

dynamical mass for the brown dwarf binary gl 417BC

Trent J. Dupuy, Michael C. Liu, Michael J. Ireland

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Abstract

We present new evidence for a problem with cooling rates predicted by substellar evolutionary models that implies that model-derived masses in the literature for brown dwarfs and directly imaged planets may be too high. Based on our dynamical mass for Gl 417BC (L4.5+L6) and a gyrochronology system age from its young, solar-type host star, commonly used models predict luminosities 0.2-0.4 dex lower than we observe. This corroborates a similar luminosity-age discrepancy identified in our previous work on the L4+L4 binary HD 130948BC, which coincidentally has nearly identical component masses (50-55 M Jup) and age (800 Myr) as Gl 417BC. Such a luminosity offset would cause systematic errors of 15%-25% in model-derived masses at this age. After comparing different models, including cloudless models that should not be appropriate for mid-L dwarfs like Gl 417BC and HD 130948BC but actually match their luminosities better, we speculate the observed overluminosity could be caused by opacity holes (i.e., patchy clouds) in these objects. Moreover, from hybrid substellar evolutionary models that account for cloud disappearance, we infer the corresponding phase of overluminosity may extend from a few hundred million years up to a few gigayears and cause masses to be overestimated by up to 25%, even well after clouds disappear from view entirely. Thus, the range of ages and spectral types affected by this potential systematic shift in luminosity evolution would encompass most known directly imaged gas-giants and field brown dwarfs.

Original languageEnglish
Article number133
Pages (from-to)1-14
Number of pages14
JournalAstrophysical Journal
Volume790
Issue number2
DOIs
Publication statusPublished - 1 Aug 2014

Bibliographical note

Copyright 2014 The American Astronomical Society. First published in the Astrophysical journal, 790(2), 133, 2014, published by IOP Publishing. The original publication is available at http://www.doi.org/10.1088/0004-637X/790/2/133. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

Keywords

  • astrometry
  • binaries: close
  • brown dwarfs
  • infrared: stars
  • stars: fundamental parameters
  • stars: individual

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