ลองค้นข้อมูลดู ได้ชื่อTau มาสองชื่อ Tau Bootis b กับ Tau Ceti Discovered in 1996, the planet is one of the first extrasolar planets found. It was discovered orbiting the star Tau Boo (HR 5185) by Paul Butler and Geoffrey Marcy (San Francisco Planet Search Project) [4] using the highly successful radial velocity method. Since the star is visually bright and the planet is massive, it produces a very strong velocity signal of 469 ± 5 metres per second, which was quickly confirmed by Michel Mayor and Didier Queloz from data collected over 15 years. It was later confirmed also by the AFOE Planet Search Team. Orbit and massEdit Tau Boötis b is rather massive, with a minimum mass over four times that of Jupiter. It orbits the star in a so-called torch orbit, at a distance from the star less than one seventh that of Mercurys from the Sun. One orbital revolution takes only 3 days 7.5 hours to complete. Because τ Boo is hotter and larger than the Sun and the planets orbit is so low, it is assumed to be hot. Assuming the planet is perfectly grey with no greenhouse or tidal effects, and a Bond albedo of 0.1, the temperature would be close to 1600 K.[6] Although it has not been detected directly, it is certain that the planet is a gas giant. As Tau Boötis b is more massive than most known hot Jupiters, it was speculated that it was originally a brown dwarf, a failed star, which could have lost most of its atmosphere from the heat of its larger companion star. However, this seems very unlikely. Still, such a process has actually been detected on the famous transiting planet HD 209458 b. In December 1999, a group led by A. C. Cameron had announced that they had detected reflected light from the planet. They calculated that the orbit of the planet has an inclination of 29° and thus the absolute mass of the planet would be about 8.5 times that of Jupiter. They also suggested that the planet is blue in color. Unfortunately, their observations could not be confirmed and were later proved to be spurious. A better estimate came from the assumption of tidal lock with the star, which rotates at 40 degrees;[7] fixing the planets mass between 6 and 7 Jupiter masses. In 2007, magnetic field detection confirmed this estimate.[8] In 2012 two teams independently distinguished the radial-velocity of the planet from the radial velocity of the star by observing the shifting of the spectral lines of carbon monoxide. This enabled calculation of the inclination of the planets orbit and hence the planets mass. One team found an inclination of 44.5±1.5degrees and a mass of 5.95±0.28MJ.[9] The other team found an inclination of 47-6+7 and a mass of 5.6±0.7MJ.[10] Tau Ceti Breaking News On December 19, 2012, a team of astronomers announced the possible detection of five planets in relatively circular orbits around Tau Ceti, with periods of 14.0, 35.4, 94.1, 168, and 642 days with a minimum of 2.0, 3.1, 3.6, 4.3, and 6.6 Earth-masses, respectively. The team applied noise modelling to subtract noise and thereby find the smallest signals hiding in the data from Tau Ceti, on which there is a lot of radial-velocity data from three different planet-hunting missions: HARPS, AAPS, and HiRes. They put in fake planets to add signals into the messy data emulating what planets would add and found ways to reduce the noise until the fake planets became more and more visible in the data, in the process of which they actually detected real signals as well. One of planetary candidates, designated HD 10700 e, lies about half as far from Tau Ceti as the Earth is from the Sun which lies in the habitable zone of Tau Ceti because it is slightly smaller and dimmer than our own Sun, Sol (press release; Ken Croswell, Science Now, December 18, 2012; BBC News, December 19, 2012; Astrobiology, December 19, 2012; and Tuomi et al, 2012).
Posted on: Sat, 13 Sep 2014 07:46:47 +0000
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