Epsilon Eridani

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Epsilon Eridani
Observation data
Equinox J2000
Constellation Eridanus
Right ascension 3h 32m 55.8s
Declination -9° 27' 29.7"
Apparent magnitude (V) 3.73
Characteristics
Spectral type K2V
U-B color index 0.59
B-V color index 0.88
Variable type BY Draconis
Astrometry
Radial velocity (Rv) 15 km/s
Proper motion (μ) RA: -976.44 mas/yr
Dec.: 17.97 mas/yr
Parallax (π) 310.75 ± 0.85 mas
Distance 10.5 ± 0.03 ly
(3.218 ± 0.009 pc)
Absolute magnitude (MV) 6.192
Details
Mass 0.85 M☉
Radius 0.84 R☉
Luminosity 0.28 L☉
Temperature 5,100 K
Metallicity 49–65% Sun
Rotation 11.1 days
Age 5 × 108 years
Other designations
18 Eri, HD 22049, HR 1084, BD-09°697, GCTP 742.00, WDS 03330-0928, SAO 130564, LHS 1557

Epsilon Eridani (ε Eri / ε Eridani) is a notable main-sequence K2 class star in the constellation of Eridanus. It has no official proper name (called only by its Bayer designation), although Arab settlers along the East African coast occasionally applied the name الصادرة Al-Sadirah "the Returning Ostriches" to the star nearly seven centuries ago.[citation needed]

Epsilon Eridani is the third closest star outside of the solar system visible without a telescope. It has 85% of the Sun's mass, is roughly the same size, but has only 28% of its luminosity, and is 10.522 light years distant.

Epsilon Eridani's most unusual characteristic is its extremely variable spectrum, with many emission lines. Futhermore, it has a very strong magnetic field and has been measured to rotate once every 12 days (roughly twice as fast as the Sun). The reason for this is its youth; it is only about half a billion years old. Despite this young age, however, it has relatively low metallicity, particularly in iron.

Its closest neighbour is Luyten 726-8 (UV Ceti and BL Ceti), 5.22 ly (1.60 pc) away.

Contents

[edit] Dust disk

In 1988, a dust disk was discovered around the star, at a similar distance as the Kuiper belt is from our Sun. Bruce Campbell and others interpreted doppler measurements as clumps in the dust ring that suggest another planet orbits the star, causing the clumps through resonance. The dust disc contains approximately 1000 times more dust than is present in the inner system around our Sun, which may mean it has about 1000 times as much cometary material as our solar system.

Within 35 AU of the star the dust is depleted, which may mean that the system has formed planets which have cleared out the dust in this region. This is consistent with currently accepted models of the inner solar system, and so there may be terrestrial planets around the star.

[edit] Planetary system

As Epsilon Eridani is one of the nearest solar-type stars to our Sun, many attempts to search for orbiting planets have been made. However, the star's high activity and variability means that finding planets with the radial velocity method is difficult, and stellar activity may mimic the presence of planets. Furthermore, the low metallicity (roughly half that of the solar system) in the system reduces the odds of planet formation. If terrestrial planets do exist, however, for liquid water to exist on the surface, the planet would have to be around 0.53 AU from the star.

[edit] Epsilon Eridani b

Epsilon Eridani b
Discovery
Discovered by: Hatzes et al.
Discovery date: 2000
Detection method(s): Radial velocity
Orbital characteristics
Semi-major axis: 3.39 ± 0.36 AU
Eccentricity: 0.702 ± 0.039
Orbital period: 2502 ± 10 d
Inclination: 30.1 ± 3.8°
Longitude of the periastron: 34°
Time of periastron: 54207 ± 7 JD
Physical characteristics
Mass: 1.55 ± 0.24 MJ

Epsilon Eridani b is an extrasolar planet candidate around Epsilon Eridani, announced in 2000 by a team led by Artie Hatzes. The discoverers gave its mass as 1.2 ± 0.33 times that of Jupiter, with a mean distance of 3.3 AU from the star. The object's orbit is highly eccentric. Other observers, including Geoffrey Marcy required more information on the star's doppler noise behaviour created by its large and varying magnetic field, and the discovery remains controversial. Its existence had also been previously suspected by a Canadian team led by Bruce Campbell and Gordon Walker in the early 1990s, but their observations weren't definitive enough to make a solid discovery.

Observations by the Hubble Space Telescope have confirmed the existence of this planet. The estimated mass is 1.5 times Jupiter's mass, and the orbit is inclined by an angle of 30° from our line of sight. This orbital inclination is parallel to the observed dust ring around the star. The planet is expected to reach periapsis in 2007, when it could potentially be observed by the Hubble telescope.[1][2]

[edit] Epsilon Eridani c

Epsilon Eridani c
Discovery
Discovered by: Quillen, Thorndike
Discovery date: 2002
Detection method(s): Analysis of dust disk
Orbital characteristics
Semi-major axis: ~40 AU
Eccentricity: ~0.3
Orbital period: ~280 y
Time of periastron: −869.74 JD
Physical characteristics
Mass: ~0.1 MJ

A hypothetical planet designated Epsilon Eridani c was proposed in 2002 based on analysis of the structure of the dust disk around the star. Clumping in the dust disk can be modelled by dust particles being trapped in resonances with a planet in an eccentric orbit. As of 2006 the existence of this planet has not been confirmed.

[edit] See also

[edit] Footnotes and references

  1. ^ "Hubble Zeroes in on Nearest Known Exoplanet", Hubble News Desk, 2006-10-09. Retrieved on October 10, 2006.
  2. ^ Benedict et al. (2006), The Extrasolar Planet ɛ Eridani b: Orbit and Mass, The Astronomical Journal, Volume 132, Issue 5, pp. 2206-2218; preprint

[edit] External links

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