Epsilon Eridani
| Observation data Epoch J2000 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 | 10.50 ± 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 | |
Epsilon Eridani (ε Eri / ε Eridani) is a main-sequence K2 class star in the constellation of Eridanus. Epsilon Eridani, 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.
Epsilon Eridani is the third closest star outside of the solar system visible without a telescope. It has 85% of the Sun's mass, almost that much of its diameter, and 28% of its luminosity.
Its spectrum is extremely variable, with many emission lines. It has a very strong magnetic field. It spins about every 11 days.[1] The reason for all this is its youth; it is only about half a billion years old. For this reason, it is considered unlikely to have intelligent life in its system. Tau Ceti is a much better candidate, and like Epsilon Eridani, is also deficient in iron. A planet orbiting Epsilon Eridani at a distance of around 0.53 astronomical units would have temperatures suitable for liquid water.
Its closest neighbour is Luyten 726-8 (UV Ceti and BL Ceti), 5.22 ly (1.60 pc) away.
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.
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.
Epsilon Eridani b
| Discovery | |
|---|---|
| Radial velocity | |
| Orbital characteristics | |
| 3.39 ± 0.36 | |
| Eccentricity | 0.702 ± 0.039 |
| 2502 ± 10 | |
| Inclination | 30.1 ± 3.8 |
| Physical characteristics | |
| Mass | 1.55 ± 0.24 |
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.[2]
Epsilon Eridani c
| Discovery | |
|---|---|
| Analysis of dust disk | |
| Orbital characteristics | |
| ~40 | |
| Eccentricity | ~0.3 |
| Inclination | ? |
| Physical characteristics | |
| Mass | ~0.1 |
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.
See also
Footnotes and references
- ^ Baliunas measured a rotation period of 12 days
- ^ "Hubble Zeroes in on Nearest Known Exoplanet". Hubble News Desk. 2006-10-09. Retrieved 2006-10-10.
- Sallie Baliunas, Dmitry Sokoloff, and Willie Soon (1996 February 1). "Magnetic Field and Rotation in Lower Main-Sequence Stars: An Empirical Time-Dependent Magnetic Bode's Relation?". Astrophysical Journal. 457 (Number 2, Part 2): L99–L102.
{{cite journal}}:|issue=has extra text (help); Check date values in:|year=(help)CS1 maint: multiple names: authors list (link) CS1 maint: year (link) - "Astronomers discover a nearby star system just like our own Solar System". JAC/UCLA. Retrieved March 24.
{{cite web}}: Check date values in:|accessdate=(help); Unknown parameter|accessyear=ignored (|access-date=suggested) (help) - Bruce Campbell, G.A.H. Walker, S. Yang (1988). "A search for substellar companions to solar-type stars". Astrophysical Journal. 331 (Part 1): 902–921.
{{cite journal}}: Check date values in:|year=(help)CS1 maint: multiple names: authors list (link) CS1 maint: year (link) - A.C. Quillen, Stephen Thorndike (2002). "Structure in the ε Eridani Dusty Disk Caused by Mean Motion Resonances with a 0.3 Eccentricity Planet at Periastron". Astrophysical Journal. 578 (2): L149–L142.
{{cite journal}}: Check date values in:|year=(help)CS1 maint: year (link)
External links
- "HD 22049". SIMBAD. Retrieved 13 April.
{{cite web}}: Check date values in:|accessdate=(help); Unknown parameter|accessyear=ignored (|access-date=suggested) (help) - "Notes for star Epsilon Eridani". The Extrasolar Planets Encyclopaedia. Retrieved 13 April.
{{cite web}}: Check date values in:|accessdate=(help); Unknown parameter|accessyear=ignored (|access-date=suggested) (help) - "Epsilon Eridani". SolStation. Retrieved 13 April.
{{cite web}}: Check date values in:|accessdate=(help); Unknown parameter|accessyear=ignored (|access-date=suggested) (help)