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09-October-2006, 04:06 PM
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The planet of Epsilon Eridani confirmed
In 2000 an extrasolar planet was announced orbiting the nearby orange dwarf Epsilon Eridani. However, the planet Epsilon Eridani b was less certain than others since the star is young (~800 million years) and therefore magnetically active which makes radial velocity measurements hard.
Now Hubble Space Telescope has been able to confirm the planet using astrometry. Code:
Epsilon Eridani b Discovered in 2000 Mass 1.55 (± 0.24) MJ Semi major axis 3.39 (± 0.36) AU Orbital period 2502 (± 10) days Eccentricity 0.702 (± 0.039) Omega 47 (± 3) deg. Tperi 54207 (± 7) JD 2.400.000 Inclination 30.1 (± 3.8) deg. Abstract of the paper describing the detection is here. Epsilon Eridani has a circumstellar dust disk not much unlike the Kuiper Belt. The shape of the disk implies another, much more distant planet. The radial velocity measurements suggest the planet really exist. The large eccentricity (0.702) of the planet b is nasty since the planet comes to 1 AU from the star. The habitable zone is closer to the star, but the planet comes terribly close the zone so any habitable planet may be disturbed.
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Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool. -- Richard Feynman 
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09-October-2006, 06:44 PM
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Quote:
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`Irony` actually does mean `metal like`...
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09-October-2006, 07:01 PM
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GJ849b a Jupiter-Mass Planet
Title: A Long-Period Jupiter-Mass Planet Orbiting the Nearby M Dwarf GJ849
Authors: R. Paul Butler, John A. Johnson, Geoffrey W. Marcy, Jason T. Wright, Steven S. Vogt, Debra A. Fischer We report precise Doppler measurements of GJ849 (M3.5V) that reveal the presence of a planet with a minimum mass of 0.82 Mjup in a 5.16 year orbit. At a = 2.35 AU, GJ849b is the first planet discovered around an M dwarf to orbit beyond 0.21 AU, and is only the second Jupiter mass planet discovered around a star less massive than 0.5 Msun. This detection brings to 4 the number of M stars known to harbor planets. Based on the results of our survey of 1300 FGKM main--sequence stars we find that giant planets within 2.5 AU are ~3 times more common around GK stars than around M stars. Due to the GJ849's proximity of 8.8 pc, the planet's angular separation is 0."27, making this system a prime target for high--resolution imaging using adaptive optics and future space--borne missions such as the Space Interferometry Mission. We also find evidence of a linear trend in the velocity time series, which may be indicative of an additional planetary companion. Read more (68kb, PDF)
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`Irony` actually does mean `metal like`...
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09-October-2006, 08:11 PM
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They've made an Hubble press release about the discovery.
__________________
Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool. -- Richard Feynman
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10-October-2006, 10:24 AM
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There are almost 200 planets found using the radial velocity method. Since the method is indirect, a few of them may be spurious. We know only their minimum masses, but simple statistics tells us that vast majority of them should be bona fide planets.
__________________
Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool. -- Richard Feynman
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