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2M1207, 2M1207A or 2MASS J12073346-3932539 is a brown dwarf located in the constellation Centaurus; a companion object, 2M1207b, may be the first extrasolar planetary-mass companion to be directly imaged, and is the first discovered orbiting a brown dwarf.〔 2M1207 was discovered during the course of the 2MASS infrared sky survey: hence the "2M" in its name, followed by its celestial coordinates. With a fairly early (for a brown dwarf) spectral type of M8,〔 it is very young, and probably a member of the TW Hydrae association. Its estimated mass is around 25 Jupiter masses.〔 The companion, 2M1207b, is estimated to have a mass of 3–10 Jupiter masses.〔(Star: 2M1207 ), ''Extrasolar Planets Encyclopaedia''. Accessed on line June 15, 2008.〕 Still glowing red hot, it will shrink to a size slightly smaller than Jupiter as it cools over the next few billion years. An initial photometric estimate for the distance to 2M1207 was 70 parsecs.〔 In December 2005, American astronomer Eric Mamajek reported a more accurate distance (53 ± 6 parsecs) to 2M1207 using the moving cluster method. The new distance gives a fainter luminosity for 2M1207. Recent trigonometric parallax results have confirmed this moving cluster distance, leading to a distance estimate of 53 ± 1 parsec or 172 ± 3 light years.〔("The Distance to the 2M1207 System" ), Eric Mamajek, November 8, 2007. Accessed on line June 15, 2008.〕 Like classical T Tauri stars, many brown dwarfs are surrounded by disks of gas and dust which accrete onto the brown dwarf.〔(More Sun-like stars may have planetary systems than currently thought ), library, Origins program, NASA. Accessed on line June 16, 2008.〕〔First Ultraviolet Spectrum of a Brown Dwarf: Evidence for H2 Fluorescence and Accretion, John E. Gizis, Harry L. Shipman, and James A. Harvin, ''Astrophysical Journal'' 630, #1 (September 2005), pp. L89–L91. .〕 2M1207 was first suspected to have such a disk because of its broad Hα line. This was later confirmed by ultraviolet spectroscopy.〔 The existence of a dust disk has also been confirmed by infrared observations.〔Spitzer Observations of Two TW Hydrae Association Brown Dwarfs, Basmah Riaz, John E. Gizis, and Abraham Hmiel, ''Astrophysical Journal'' 639, #2 (March 2006), pp. L79–L82. .〕 In general, accretion from disks is known to produce fast-moving jets, perpendicular to the disk, of ejected material.〔Accretion-ejection models of astrophysical jets, R. E. Pudritz, in ''Accretion Disks, Jets and High-energy Phenomena in Astrophysics'', Vassily Beskin, Gilles Henri, Francois Menard, Guy Pelletier, and Jean Dalibard, eds., NATO Advanced Study Institute, Les Houches, session LXXVIII, EDP Sciences/Springer, 2003. ISBN 3-540-20171-8.〕 This has also been observed for 2M1207; an April 2007 paper in the ''Astrophysical Journal'' reports that this brown dwarf is spouting jets of material from its poles. The jets, which extend around 109 kilometers into space, were discovered using the Very Large Telescope (VLT) at the European Southern Observatory. Material in the jets streams into space at a few kilometers per second.〔(Small Stars Create Big Fuss ), Ker Than, May 28, 2007, space.com. Accessed on line June 15, 2008.〕 == See also == * Direct imaging of extrasolar planets * List of extrasolar planets 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「2M1207」の詳細全文を読む スポンサード リンク
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