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? Indi Ba, Bb: a detailed study of the nearest known brown dwarfs
The discovery of ? Indi Ba, Bb, a binary brown dwarf system veryclose to the Sun, makes possible a concerted campaign to characterisethe physical parameters of two T dwarfs. Recent observations suggestsubstellar atmospheric and evolutionary models may be inconsistent withobservations, but there have been few conclusive tests to date. Wetherefore aim to characterise these benchmark brown dwarfs to placeconstraints on such models. We have obtained high angular resolutionoptical, near-infrared, and thermal-infrared imaging andmedium-resolution (up to R ~ 5000) spectroscopy of ? Indi Ba, Bbwith the ESO VLT and present VRIzJHKL'M' broad-band photometry and0.63-5.1 ?m spectroscopy of the individual components. The photometryand spectroscopy of the two partially blended sources were extractedwith a custom algorithm. Furthermore, we use deep AO-imaging to placeupper limits on the (model-dependent) mass of any further systemmembers. We derive luminosities of log L/L? = -4.699±0.017 and -5.232 ±0.020 for ? Indi Ba, Bb,respectively, and using the dynamical system mass and COND03evolutionary models predict a system age of 3.7-4.3 Gyr, in excess ofprevious estimates and recent predictions from observations of thesebrown dwarfs. Moreover, the effective temperatures of 1352-1385 K and976-1011 K predicted from the COND03 evolutionary models, for ?Indi Ba and Bb respectively, are in disagreement with those derived fromthe comparison of our data with the BT-Settl atmospheric models where wefind effective temperatures of 1300-1340 K and 880-940 K, for ?Indi Ba and Bb respectively, with surface gravities of log g = 5.25 and5.50. Finally, we show that spectroscopically determined effectivetemperatures and surface gravities for ultra-cool dwarfs can lead tounderestimated masses even where precise luminosity constraints areavailable.Based on observations collected with the ESO VLT, Paranal, Chile underprogram 072.C-0689The full resolution spectra of both brown dwarfs are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/510/A99
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