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Issue A&A
Volume 436, Number 2, June III 2005
Page(s) L39 - L42
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200500121



A&A 436, L39-L42 (2005)
DOI: 10.1051/0004-6361:200500121

Letter

The cool atmospheres of the binary brown dwarf $\varepsilon$ Indi B

M. F. Sterzik1, E. Pantin1, 2, M. Hartung1, N. Huelamo1, H. U. Käufl3, A. Kaufer1, C. Melo1, D. Nürnberger1, R. Siebenmorgen3 and A. Smette1

1  European Southern Observatory, Casilla 19001, Santiago 19, Chile
    e-mail: msterzik@eso.org
2  DSM/DAPNIA/Service d'Astrophysique, CEA/Saclay, 91191 Gif-sur-Yvette, France
3  European Southern Observatory, 85748 Garching b. München, Germany

(Received 15 March 2005 / Accepted 30 April 2005)

Abstract
We have imaged $\varepsilon$ Indi B, the closest brown dwarf binary known, with VISIR at the VLT in three narrow-band mid-infrared bandpasses located around 8.6 $\mu$m, 10.5 $\mu$m and 11.3 $\mu$m. We are able to spatially resolve both components, and determine accurate mid-infrared photometry for both components independently. In particular, our VISIR observations probe the NH3 feature in the atmospheres of the cooler and warmer brown dwarfs. For the first time, we can disentangle the contributions of the two components, and find that $\varepsilon$ IndiBb is in good agreement with recent "cloud-free" atmosphere models having an effective temperature of Teff =800 K. With an assumed age of 1 Gyr for the $\varepsilon$ Indi system, component Ba agrees more with $T_\mathrm{eff} \approx 1100$ K rather than with Teff=1200 K, as suggested by SPITZER spectroscopic observations of the combined $\varepsilon$ Indi B system (Roellig et al. 2004). Even higher effective temperatures appear inconsistent with our absolute photometry, as they would imply an unphysical small size of the brown dwarf $\varepsilon$ IndiBa.


Key words: stars: low-mass, brown dwarfs -- stars: binaries: general

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© ESO 2005


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