Discovery of a Brown Dwarf Very Close to the Sun: A Methane-rich Brown Dwarf Companion to the Low-Mass Star SCR 1845–6357

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 (1170 ± 0003 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 (absolute H magnitude of 15.30), 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 Indi Ba-Bb (at 3.626 pc). In addition, this is the first T dwarf companion discovered around a low-mass star.

[1]  Gordon A. H. Walker,et al.  Speckle Noise and the Detection of Faint Companions , 1999 .

[2]  C. Marois,et al.  Efficient Speckle Noise Attenuation in Faint Companion Imaging , 2000 .

[3]  Rene Doyon,et al.  Differential imaging coronagraph for the detection of faint companions , 2000, Astronomical Telescopes and Instrumentation.

[4]  A. Burrows,et al.  The theory of brown dwarfs and extrasolar giant planets , 2001, astro-ph/0103383.

[5]  B. Reipurth,et al.  The Formation of Brown Dwarfs as Ejected Stellar Embryos , 2001, astro-ph/0103019.

[6]  et al,et al.  Toward Spectral Classification of L and T Dwarfs: Infrared and Optical Spectroscopy and Analysis , 2001, astro-ph/0108443.

[7]  Adam Burrows,et al.  Beyond the T Dwarfs: Theoretical Spectra, Colors, and Detectability of the Coolest Brown Dwarfs , 2003, astro-ph/0304226.

[8]  M. Skrutskie,et al.  The 2Mass Wide-Field T Dwarf Search. I. Discovery of a Bright T Dwarf within 10 Parsecs of the Sun , 2002, astro-ph/0211117.

[9]  David Mouillet,et al.  NAOS, the first AO system of the VLT: on-sky performance , 2003, SPIE Astronomical Telescopes + Instrumentation.

[10]  Laird M. Close,et al.  Detection of Nine M8.0-L0.5 Binaries: The Very Low Mass Binary Population and Its Implications for Brown Dwarf and Very Low Mass Star Formation , 2003, astro-ph/0301095.

[11]  Anne-Marie Lagrange,et al.  NAOS-CONICA first on sky results in a variety of observing modes , 2003, SPIE Astronomical Telescopes + Instrumentation.

[12]  Tucson,et al.  ε Indi Ba,Bb: The nearest binary brown dwarf , 2003, astro-ph/0309256.

[13]  G. Knapp,et al.  Hubble Space Telescope Observations of Binary Very Low Mass Stars and Brown Dwarfs , 2003, astro-ph/0302526.

[14]  P. H. Hauschildt,et al.  Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 209458 , 2003 .

[15]  The Solar Neighborhood. VIII. Discovery of New High Proper Motion Nearby Stars Using the SuperCOSMOS Sky Survey , 2004, astro-ph/0404265.

[16]  The Solar Neighborhood. X. New Nearby Stars in the Southern Sky and Accurate Photometric Distance Estimates for Red Dwarfs , 2004, astro-ph/0408240.

[17]  et al,et al.  Near-Infrared Photometry and Spectroscopy of L and T Dwarfs: The Effects of Temperature, Clouds, and Gravity , 2004, astro-ph/0402451.

[18]  D. A. Golimowski,et al.  Preliminary Parallaxes of 40 L and T Dwarfs from the US Naval Observatory Infrared Astrometry Program , 2004 .

[19]  Laird M. Close,et al.  A novel simultaneous differential imager for the direct imaging of giant planets , 2004, SPIE Astronomical Telescopes + Instrumentation.

[20]  Tom Herbst,et al.  A new VLT surface map of Titan at 1.575 microns , 2004 .

[21]  M. Mugrauer,et al.  Accepted Received , 2005 .

[22]  R. Lenzen,et al.  AB Doradus C: age, spectral type, orbit, and comparison to evolutionary models , 2005 .

[23]  Laird M. Close,et al.  A dynamical calibration of the mass–luminosity relation at very low stellar masses and young ages , 2005, Nature.

[24]  C. Marois,et al.  TRIDENT: an Infrared Differential Imaging Camera Optimized for the Detection of Methanated Substellar Companions , 2005 .

[25]  The Solar Neighborhood. XI. The Trigonometric Parallax of SCR 1845−6357 , 2004, astro-ph/0409582.