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Beta Pictoris b is an exoplanet located approximately 63 light-years away in the constellation of Pictor, orbiting the 4th magnitude debris disk star Beta Pictoris. It has a mass between 4 and 11 Jupiter masses and a radius around 65% larger than Jupiter's. It orbits at 9 AU from Beta Pictoris (close to the plane of the debris disk orbiting the star) with a low eccentricity and a period of 20–21 years, and is the only known planet in the Beta Pictoris system. The planet was discovered on November 18, 2008 by Lagrange ''et al.'', using the NACO instrument on the Very Large Telescope at Cerro Paranal in northern Chile. This planet was discovered using the direct imaging technique, utilizing reference star differential imaging. The discovery image was taken in 2003, but the planet was not detected when the data were first reduced. A re-reduction of the data in 2008 using modern image processing tools revealed the faint point source now known to be a planet. Follow-up observations performed in late 2009 and early 2010 using the same instrument recovered and confirmed the planet, but on the opposite side of the star. These findings were published in the journal Science and represented the closest orbiting planet to its star ever imaged. Observations performed in late 2010 and early 2011 allowed scientists to establish an inclination angle of the planet's orbit of 88.5 degrees, nearly edge-on. The location of the planet was found to be approximately 3.5 to 4 degrees tilted from the main disk in this system, indicating that the planet is aligned with the warped inner disk in the Beta Pictoris system.〔 The first study of the spectral energy distribution of the planet was published in July 2013. This study shows detections at 1.265, 1.66, 2.18, 3.80, 4.05 and 4.78 µm demonstrating that the planet has a very dusty and/or cloudy atmosphere. The SED is consistent with that of an early L dwarf, but with a lower surface gravity. The effective temperature is constrained to and the surface gravity to log g = 4.0 . A second study, published in September 2013,〔 provided a new detection at 3.1 µm obtained at the Gemini Observatory along with a reanalysis of previous data. They found the planet to be overluminous in the mid-infrared 3.1 µm band compared to models of early L dwarfs. Models incorporating small dust particles and thick clouds provided the best fit to the SED. The effective temperature is constrained to and the surface gravity to log g = 3.8 . This fit corresponds to a planet radius of 1.65 times that of Jupiter, arguing that Beta Pictoris b may be younger than its host star (finished forming at 5 Ma). In 2014, the rotation period of Beta Pictoris b was calculated from the broadening of its carbon monoxide infrared absorption line. This makes it, , the first extrasolar planet to have its rotation rate measured. With a rotation period of 8.1 hours, it is the fastest-spinning planet known. In 2015, a short video was made from direct images of Beta Pictoris b taken by the Gemini Planet Imager over the course of about two years showing a time-lapse of the planet orbitng around its parent star. ==References== 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「Beta Pictoris b」の詳細全文を読む スポンサード リンク
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