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| - Mid-infrared followup of cold brown dwarfs: Diversity in age, mass and metallicity
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| - We use Spitzer IRAC 3.6-8.0 μm photometry of late-type T dwarfs to investigate various trends which can aid the planning and interpretation of infrared (IR) surveys for the coldest T or Y dwarfs. Brown dwarfs with effective temperature ( Teff)<700 K emit>50% of their flux at λ>3 μ m, and the ratio of the mid-IR to the near-IR flux becomes very sensitive to Teff. The color H − [4.5] is a good indicator of Teff with a weak dependence on metallicity ([m/H]) and gravity ( g) while H − K and [4.5] − [5.8] are sensitive to [m/H] and g. Thus Teff and g can be constrained and mass and age can then be determined from evolutionary models. There are 12 dwarfs known with H − [4.5] > 3.0 and 500 ≲ TeffK ≲ 800, which we examine in detail. The ages of these dwarfs range from very young (0.1-1.0 Gyr) to old (3-12 Gyr). The mass range is possibly as low as 5 M Jup to 70 M Jup, and [m/H] also spans a large range of ~ −0.3 to ~ +0.3. The T8-T9 dwarfs found so far in the UKIRT IR Deep Sky Survey are unexpectedly young and low-mass. Extensions to the warm Spitzer and WISE space missions are needed to obtain mid-IR data for cold brown dwarfs, and to discover more of these rare objects.
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| - © Owned by the authors, published by EDP Sciences, 2011
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| - Owned by the authors, published by EDP Sciences
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