Epsilon Eridani
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| Observation data Epoch J2000 |
|
|---|---|
| Constellation (pronunciation) |
Eridanus |
| Right ascension | 03h 32m 55.8442s[1] |
| Declination | −09° 27′ 29.744 ″[1] |
| Apparent magnitude (V) | 3.73[1] |
| Characteristics | |
| Spectral type | K2V[1] |
| U-B color index | +0.58[2] |
| B-V color index | +0.88[2] |
| V-R color index | +0.50 |
| R-I color index | +0.42 |
| Variable type | BY Draconis |
| Astrometry | |
| Radial velocity (Rv) | +15.5±0.9[1] km/s |
| Proper motion (μ) | RA: −976.36[1] mas/yr Dec.: 17.98[1] mas/yr |
| Parallax (π) | 310.74 ± 0.85[1] mas |
| Distance | 10.5 ± 0.03 ly (3.218 ± 0.009 pc) |
| Absolute magnitude (MV) | 6.19[3] |
| Details | |
| Mass | 0.85[3] M☉ |
| Radius | 0.84[4] R☉ |
| Surface gravity (log g) | 4.57[5] |
| Luminosity | 0.28 L☉ |
| Temperature | 5073±42[6] K |
| Metallicity | [Fe/H]=−0.13±0.04[6] |
| Rotation | 11.1 days |
| Age | 5 × 108 years |
| Other designations | |
Epsilon Eridani (ε Eri / ε Eridani) is a notable main-sequence K2 class star. It is the closest star in the constellation of Eridanus at 10.5 light years from the Solar System and is the third closest star visible to the naked eye.
Epsilon Eridani has no official proper name (being 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]
Due to it being a relatively close and sun-like star, Epsilon Eridani regularly appears in science fiction. Its closest neighbour is Luyten 726-8 (UV Ceti and BL Ceti), 5.22 ly (=1.60 pc) away.
Contents |
[edit] Properties
Epsilon Eridani has an estimated 85% of the Sun's mass[3] and 84% of the Sun's radius,[4] but has only 28% of its luminosity and is 10 light years distant. It is the second nearest spectral class K star after α Centauri B.[3] Compared to the Sun, this star is considered slightly low in the abundance of elements with atomic numbers higher than helium. Epsilon Eridani has only about 74% of the Sun's abundance of iron in its chromosphere.[6]
The star's most unusual characteristic is its extremely variable spectrum, with many emission lines. Furthermore, 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 as it is only about 800 million to a billion years old.
[edit] Dust disk
In 1998, a dust disk was discovered around the star, at a similar distance as the Kuiper belt is from our Sun. Astronomers 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. Epsilon Eridani is the target for many planet finding programs because it has the properties to allow an Earthlike planet to form. For liquid water to exist on the surface of a habitable planet ranging from 1 to 2.5 earth masses, the planet would have to be around 0.53 to 0.80 AU from the star. If humans were to find an earthlike planet it might need terraformation in order for humans to live on it due to the system's age.
There are two planets in the system, one confirmed and one unconfirmed. A 2500 day-period Jupiter-like planet Epsilon Eridani b orbits at 3.39 AU in one of the most eccentric orbit of any extrasolar planets — 0.7. A 280 year-period low-mass planet Epsilon Eridani c orbits at 40 AU in a less eccentric orbit — 0.3.
| Planet (in order from star) |
Mass (MJ) |
Orbital period (days) |
Semimajor axis (AU) |
Eccentricity |
|---|---|---|---|---|
| b | 1.55 ± 0.24 | 2502 ± 10 | 3.39 ± 0.36 | 0.702 ± 0.039 |
| "c" | ~0.1 | ~102200 | ~40 | ~0.3 |
[edit] Closest Neighbors
| Star System | Spectra and Luminosity | Distance (light-years) |
|---|---|---|
| Hip 15689 | ? | 4.1 |
| Luyten 726-8 | M5.6 Ve | 5.1 |
| Tau Ceti | G8 Vp | 5.5 |
| Teegarden's Star | M6.5 V | 5.8 |
| Omicron2 Eridani 3 | K1 Ve DA4/VII/M4.5 Ve | 6.4 |
| LHS 1565 | M5.5 V | 6.9 |
| YZ Ceti | M4.5 Ve | 7.0 |
| Sirius 2 | A0-1 Vm/DA2-5/VII | 7.8 |
| L 1159-16 | M4.5 Ve | 8.0 |
| LP 944-20 | brown dwarf | 8.3 |
| Kapteyn's Star | M0-1.5-3 VI | 8.5 |
| LP 656-38 | M3.5 V | 9.0 |
| Ross 614 AB | M4.5 Ve | 9.4 |
| Van Maanen's Star | DF-G/VII | 9.9 |
[edit] See also
[edit] Footnotes and references
- ^ a b c d e f g h i HD 22049 -- Variable of BY Dra type. SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved on 2007-11-29.
- ^ a b Mendoza, E. E.; Gomez, V. T.; Gonzalez, S. (1978). "UBVRI photometry of 225 Am stars.". Astronomical Journal 83: 606-614.
- ^ a b c d Staff (June 8, 2007). The One Hundred Nearest Star Systems. Research Consortium on Nearby Stars. Retrieved on 2007-11-29.
- ^ a b Johnson, H. M.; Wright, C. D. (1983). "Predicted infrared brightness of stars within 25 parsecs of the sun". Astrophysical Journal Supplement Series 53: 643-711.—see p. 653.
- ^ Zhao, G.; Chen, Y. Q.; Qiu, H. M.; Li, Z. W. (2002). "Chemical Abundances of 15 Extrasolar Planet Host Stars". The Astronomical Journal 124 (4): 2224 - 2232. doi:.
- ^ a b c Santos, N. C.; Israelian, G.; Mayor, M. (2004). "Spectroscopic [Fe/H] for 98 extra-solar planet-host stars: Exploring the probability of planet formation". Astronomy & Astrophysics 415: 1153-1166.—the percentage of iron is given by
, or 74%
- Sallie Baliunas, Dmitry Sokoloff, and Willie Soon (1996). "Magnetic Field and Rotation in Lower Main-Sequence Stars: An Empirical Time-Dependent Magnetic Bode's Relation?". The Astrophysical Journal 457 (Number 2, Part 2): L99 – L102. doi:.
- Astronomers discover a nearby star system just like our own Solar System. JAC/UCLA. Retrieved on 24 March, 2005.
- 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.
- 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.
- Sean Moran, Marc Kuchner, and Matthew Holman (2004). "The Dynamical Influence of a Planet at Semimajor Axis 3.4 AU on the Dust around ε Eridani". The Astrophysical Journal 612: 1163 – 1170. doi:.
[edit] External links
- Notes for star Epsilon Eridani. The Extrasolar Planets Encyclopaedia. Retrieved on 13 April, 2006.
- Epsilon Eridani. SolStation. Retrieved on 13 April, 2006.
