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Title: The luminosities of the coldest brown dwarfs

In recent years, brown dwarfs have been extended to a new Y-dwarf class with effective temperatures colder than 500 K and masses in the range of 5-30 Jupiter masses. They fill a crucial gap in observable atmospheric properties between the much colder gas-giant planets of our own solar system (at around 130 K) and both hotter T-type brown dwarfs and the hotter planets that can be imaged orbiting young nearby stars (both with effective temperatures in the range of 1500-1000 K). Distance measurements for these objects deliver absolute magnitudes that make critical tests of our understanding of very cool atmospheres. Here we report new distances for nine Y dwarfs and seven very late T dwarfs. These reveal that Y dwarfs do indeed represent a continuation of the T-dwarf sequence to both fainter luminosities and cooler temperatures. They also show that the coolest objects display a large range in absolute magnitude for a given photometric color. The latest atmospheric models show good agreement with the majority of these Y-dwarf absolute magnitudes. This is also the case for WISE0855-0714, the coldest and closest brown dwarf to the Sun, which shows evidence for water ice clouds. However, there are also some outstanding exceptions,more » which suggest either binarity or the presence of condensate clouds. The former is readily testable with current adaptive optics facilities. The latter would mean that the range of cloudiness in Y dwarfs is substantial with most hosting almost no clouds—while others have dense clouds, making them prime targets for future variability observations to study cloud dynamics.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6]
  1. School of Physics, UNSW Australia, NSW 2052 (Australia)
  2. Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington DC 20005 (United States)
  3. Infrared Processing and Analysis Center, MS100-22, California Institute of Technology, Pasadena, CA 91125 (United States)
  4. Department of Physics and Astronomy, The University of Toledo, OH 43606 (United States)
  5. Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)
  6. Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1547 (United States)
Publication Date:
OSTI Identifier:
22369976
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 796; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COLOR; DISTANCE; DWARF STARS; EXCEPTIONS; HEAT EXCHANGERS; ICE; LUMINOSITY; MASS; OPTICS; SOLAR SYSTEM; SUN; WATER