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Distances, Luminosities, and Temperatures of the Coldest Known Substellar Objects

Science  27 Sep 2013:
Vol. 341, Issue 6153, pp. 1492-1495
DOI: 10.1126/science.1241917

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Assessing Brown Dwarfs

The last 2 years have seen the detection of dozens of very cold brown dwarfs. At temperatures around 300 to 500 kelvin, brown dwarfs are expected to have masses comparable to those of gas-giant planets, but because their distances are unknown, it has not been possible to estimate their masses. Dupuy and Kraus (p. 1492, published online 5 September) used data from the Spitzer Space Telescope to measure accurate distances to very cold brown dwarfs, which allowed them to determine the dwarfs' luminosities, temperatures, and masses. The results strengthen the connection between the coolest brown dwarfs and gas-giant exoplanets.

Abstract

The coolest known brown dwarfs are our best analogs to extrasolar gas-giant planets. The prolific detections of such cold substellar objects in the past 2 years have spurred intensive follow-up, but the lack of accurate distances is a key gap in our understanding. We present a large sample of precise distances based on homogeneous mid-infrared astrometry that robustly establishes absolute fluxes, luminosities, and temperatures. The coolest brown dwarfs have temperatures of 400 to 450 kelvin and masses almost equal to 5 to 20 times that of Jupiter, showing they bridge the gap between hotter brown dwarfs and gas-giant planets. At these extremes, spectral energy distributions no longer follow a simple correspondence with temperature, suggesting an increasing role of other physical parameters, such as surface gravity, vertical mixing, clouds, and metallicity.

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