Weather on Other Worlds. IV. Hα Emission and Photometric Variability Are Not Correlated in L0-T8 Dwarfs

Paulo A. Miles-Páez, Stanimir A. Metchev, Aren Heinze, Dániel Apai

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


Recent photometric studies have revealed that surface spots that produce flux variations are present on virtually all L and T dwarfs. Their likely magnetic or dusty nature has been a much-debated problem, the resolution to which has been hindered by paucity of diagnostic multi-wavelength observations. To test for a correlation between magnetic activity and photometric variability, we searched for Hα emission among eight L3-T2 ultra-cool dwarfs with extensive previous photometric monitoring, some of which are known to be variable at 3.6 μm or 4.5 μm. We detected Hα only in the non-variable T2 dwarf 2MASS J12545393-0122474. The remaining seven objects do not show Hα emission, even though six of them are known to vary photometrically. Combining our results with those for 86 other L and T dwarfs from the literature show that the detection rate of Hα emission is very high (94%) for spectral types between L0 and L3.5 and much smaller (20%) for spectral types ≥L4, while the detection rate of photometric variability is approximately constant (30%-55%) from L0 to T8 dwarfs. We conclude that chromospheric activity, as evidenced by Hα emission, and large-amplitude photometric variability are not correlated. Consequently, dust clouds are the dominant driver of the observed variability of ultra-cool dwarfs at spectral types, at least as early as L0.

Original languageEnglish (US)
Article number83
JournalAstrophysical Journal
Issue number2
StatePublished - May 10 2017


  • brown dwarfs
  • stars: activity
  • stars: low-mass
  • stars: rotation
  • stars: variables: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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