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Title:
Discovery of a Brown Dwarf Very Close to the Sun: A Methane-rich Brown Dwarf Companion to the Low-Mass Star SCR 1845-6357
Authors:
Biller, B. A.; Kasper, M.; Close, L. M.; Brandner, W.; Kellner, S.
Affiliation:
AA(Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721; , .), AB(European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany; .), AC(Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721; , .), AD(Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany; .), AE(W. M. Keck Observatory, 65-1120 Mamalahoa Highway, Kamuela, HI 96743; .)
Publication:
The Astrophysical Journal, Volume 641, Issue 2, pp. L141-L144. (ApJL Homepage)
Publication Date:
04/2006
Origin:
UCP
ApJ Keywords:
Stars: Binaries: Close, Instrumentation: Adaptive Optics, Stars: Imaging, Stars: Low-Mass, Brown Dwarfs
DOI:
10.1086/504256
Bibliographic Code:
2006ApJ...641L.141B

Abstract

We present VLT/NACO SDI images of the very nearby star SCR 1845-6357 (hereafter SCR 1845). SCR 1845 is a recently discovered M8.5 star just 3.85 pc from the Sun. Using the capabilities of the unique SDI device, we discovered a substellar companion to SCR 1845 at a separation of 4.5 AU (1.170"+/-0.003" on the sky) and fainter by 3.57+/-0.057 mag in the 1.575 μm SDI filter. This substellar companion has an H magnitude of 13.16+0.31-0.26 (absolute H magnitude of 15.30+0.31-0.26), making it likely the brightest mid-T dwarf known. The Simultaneous Differential Imager (SDI) consists of three narrowband filters placed around the 1.6 μm methane absorption feature characteristic of T dwarfs (Teff<1200 K). The flux of the substellar companion drops by a factor of 2.7+/-0.1 between the SDI F1 (1.575 μm) and F3 (1.625 μm) filters, consistent with strong methane absorption in a substellar companion. We estimate a spectral type of T5.5+/-1 for the companion based on the strength of this methane break. The chances that this object is a background T dwarf are vanishingly small-and there is no isolated background T dwarf in this part of the sky, according to 2MASS. Thus, it is a bound companion, hereafter SCR 1845B. For an age range of 100 Myr to 10 Gyr and spectral type range of T4.5-T6.5, we find a mass range of (9-65)MJup for SCR 1845B from the Baraffe et al. ``COND'' models. SCR 1845AB is the 24th-closest stellar system to the Sun (at 3.85 pc); the only brown dwarf system closer to the Sun is the binary brown dwarf ɛ Indi Ba-Bb (at 3.626 pc). In addition, this is the first T dwarf companion discovered around a low-mass star.

Based on observations collected at the European Southern Observatory, Paranal, Chile, through proposal 075.C-0357(A).

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