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081024-epsilon-system-01.jpg
This artist's diagram compares the Epsilon Eridani system to our own solar system. The two systems are structured similarly, and both host asteroids (brown), comets (blue) and planets (white dots).
Credit: NASA/JPL-Caltech
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Astronomers have discovered that the nearby star Epsilon Eridani has two rocky asteroid belts and an outer icy ring, making it a triple-ring system. The inner asteroid belt is a virtual twin of the belt in our solar system, while the outer asteroid belt holds 20 times more material. Moreover, the presence of these three rings of material implies that unseen planets confine and shape them.
The star Epsilon Eridani is slightly smaller and cooler than the Sun. It is located about 10.5 light-years from Earth in the constellation Eridanus. (A light-year is the distance light travels in one year, or about 6 trillion miles.) Epsilon Eridani is the ninth closest star to the Sun and is visible to the unaided eye. It is also younger than the Sun, with an approximate age of 850 million years.

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Title: Modelling epsilon Eridani and asteroseismic tests of element diffusion
Authors: Ning Gai, Shao-Lan Bi, Yan-Ke Tang

Taking into account the helium and metal diffusion, we explore the possible evolutionary status and perform seismic analysis of MOST target: the star $\epsilon$ Eridani. We adopt the different input parameters to construct the models by fitting the available observational constraints: e.g., T_{eff}, L, R, [Fe/H]. From computation, we obtain the average large spacings of epsilon Eridani about 194 1 \muHz. The age of the diffused models has been found to be about 1 Gyr, which is younger than one determined previously by models without diffusion. We found that the effect of pure helium diffusion on the internal structure of the young low-mass star is slight, but the metal diffusion influence is obvious. The metal diffusion leads the models to have much higher temperature in the radiation interior, correspondingly the higher sound speed in the interior of the model, thereby the larger frequency and spacings.

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Epsilon Eridani has long captivated the attention of science fiction writers, as well as astronomers. In 1960, years before the first extrasolar planet was detected, astronomer Frank Drake listened for radio transmissions from inhabitants of any possible planets around Epsilon Eridani as part of Project Ozma's search for intelligent extraterrestrial life. In the fictional "Star Trek" universe, Epsilon Eridani is considered by some fans to be the parent star for the planet Vulcan, Mr. Spock's home.
Although Hubble and other telescopes cannot image the gas giant planet now, they may be able to snap pictures of it in 2007, when its orbit is closest to Epsilon Eridani. The planet may be bright enough in reflected sunlight to be imaged by Hubble, other space-based cameras, and large ground-based telescopes.

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Title: The corona and upper transition region of epsilon Eridani
Authors: J.-U. Ness, C. Jordan

We present analyses of observations of epsilon Eridani (K2 V) made with the Low Energy Transmission Grating Spectrometer on Chandra and the Extreme Ultraviolet Explorer, supplemented by observations made with the Space Telescope Imaging Spectrograph, the Far Ultraviolet Spectroscopic Explorer and the Reflection Grating Spectrometer on XMM-Newton. The observed emission lines are used to find relative element abundances, to place limits on the electron densities and pressures and to determine the mean apparent emission measure distribution. As in the previous paper by Sim & Jordan (2003a), the mean emitting area as a function of the electron temperature is derived by comparisons with a theoretical emission measure distribution found from energy balance arguments. The final model has a coronal temperature of 3.4 x 10^6 K, an electron pressure of 1.3 x 10^16 cm^-3 K at T_e = 2 x 10^5 K and an area filling factor of 0.14 at 3.2 x 10^5 K. We discuss a number of issues concerning the atomic data currently available. Our analyses are based mainly on the latest version of CHIANTI (v5.2). We conclude that the Ne/O relative abundance is 0.30, larger than that recommended from solar studies, and that there is no convincing evidence for enhanced coronal abundances of elements with low first ionisation potentials.

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