Epsilon Eridani (ε Eri, ε Eridani) is a star in the southern constellation Eridanus, along a declination 9.46° south of the celestial equator. This allows it to be viewed from most of Earth's surface. At a distance of 10.5 light years (ly), it has an apparent magnitude of 3.73. It is the third closest individual star or star system visible to the unaided eye and was the closest star known to host a planet until the unconfirmed discovery of Alpha Centauri Bb. Its age is estimated at less than a billion years. Because of its youth, Epsilon Eridani has a higher level of magnetic activity than the present-day Sun, with a stellar wind 30 times as strong. Its rotation period is 11.2 days at the equator. Epsilon Eridani is smaller and less massive than the Sun, and has a comparatively lower level of elements heavier than helium. It is a main-sequence star of spectral class K2, which means that energy generated at the core through nuclear fusion of hydrogen is emitted from the surface at a temperature of about 5,000 K, giving it an orange hue.
The motion of Epsilon Eridani along the line of sight to Earth, known as the radial velocity, has been regularly observed for more than twenty years. Periodic changes in this data yielded evidence of a giant planet orbiting Epsilon Eridani, making it one of the nearest extrasolar systems with a candidate exoplanet. This object, Epsilon Eridani b, was formally announced in 2000 by a team of astronomers led by Artie Hatzes. Current data indicate that this planet orbits with a period of about 7 years at a mean separation of 3.4 astronomical units (AU), where 1 AU is the mean distance between the Earth and the Sun. Although this discovery has been controversial because of the amount of background noise in the radial velocity data, many astronomers now regard the planet as confirmed.
The system includes two belts of rocky asteroids: one at about 3 AU and a second at about 20 AU, whose structure may be maintained by a hypothetical second planet, Epsilon Eridani c. Epsilon Eridani harbors an extensive outer debris disk of remnant planetesimals left over from the system's formation.
Epsilon Eridani's designation was established in 1603 by Johann Bayer. It may be a member of the Ursa Major Moving Group of stars that share a similar motion through the Milky Way, implying these stars shared a common origin in an open cluster. Its nearest neighbor, the binary star system Luyten 726-8, will have a close encounter with Epsilon Eridani in approximately 31,500 years when they will be separated by about 0.93 ly. As one of the nearest Sun-like stars with the potential for a planet that may harbor life, Epsilon Eridani has been the target of SETI searches. Epsilon Eridani appears in science fiction stories and has been suggested as a destination for interstellar travel.
- 1 Observation history
- 2 Distance
- 3 Properties
- 4 Planetary system
- 5 See also
- 6 Notes and references
- 7 External links
Epsilon Eridani is known to astronomers at least from the 2nd century, when it was included by Claudius Ptolemy, a Greek astronomer from Alexandria, Egypt, in his catalogue of more than 1000 stars. The catalogue was included as the 7th (northern sky) and 8th (southern sky) books of his 13-book astronomical treatise Μαθηματικὴ Σύνταξις (Mathēmatikē Syntaxis), known by its later Arabic name Almagest. Constellation Eridanus, named by Ptolemy "Ποταμού" ("River"), was included in the 8th book as the 9th constellation (or 36th from the beginning), and Epsilon Eridani was the 13th star, listed in the River. Ptolemy called Epsilon Eridani "ό τών δ προηγούμενοσ" (here "δ" is number "4"), which means in Greek "a foregoing of the four". The "four" is a group of four stars in Eridanus: γ, π, δ and ε (10th–13th), of which ε is the most western, and thus, the first of the four in the apparent daily motion of the sky from east to west. The modern designations of its entry in Ptolemy's catalogue are "P 784" (in order of appearance) and "Eri 13". The magnitude, assigned to Epsilon Eridani by Ptolemy, was 3.
Epsilon Eridani was included in star catalogues of medieval Islamic astronomical treatises, which were based on Ptolemy's catalogue: in Al-Sufi's Book of Fixed Stars, published in 964, Al-Biruni's Mas'ud Canon, published in 1030, and Ulugh Beg's Zij-i Sultani, published in 1437. Al-Sufi's estimate of Epsilon Eridani's magnitude was 3. Al-Biruni quotes magnitudes from Ptolemy and Al-Sufi (however, for Epsilon Eridani he quotes the value 4 for both Ptolemy's and Al-Sufi's magnitudes, whereas original values of both these magnitudes are 3). Its number in order of appearance is 786. Ulugh Beg carried out new measurements of Epsilon Eridani's coordinates in his observatory at Samarkand, and quotes magnitudes from Al-Sufi (3 for Epsilon Eridani). The modern designations of its entry in Ulugh Beg's catalogue are "U 781" and "Eri 13" (the latter is the same as Ptolemy's catalogue designation).
In 1598 Epsilon Eridani was included in Tycho Brahe's star catalogue, republished also in 1627 by Johannes Kepler as part of his Rudolphine Tables. This catalogue was based on Tycho Brahe's observations including those on the island of Hven at his observatories Uraniborg and Stjerneborg, during 1577—1597. The sequence number of Epsilon Eridani in constellation Eridanus was 10, and it was designated "Quae omnes quatuor antecedit", which means in Latin "Which precedes all four"; the meaning is the same as Ptolemy's designation. Brahe assigned it magnitude 3.
Epsilon Eridani's Bayer designation was established in 1603 as part of the Uranometria, a star catalogue produced by German celestial cartographer Johann Bayer. His catalogue assigned letters from the Greek alphabet to groups of stars belonging to the same visual magnitude class in each constellation, beginning with alpha (α) for a star in the brightest class. However, Bayer made no attempt to arrange stars by relative brightness within each class. Thus, although Epsilon is the fifth letter in the Greek alphabet, the star is the tenth brightest star in Eridanus. In addition to the letter ε, Bayer had given it the number 13 (the same as Ptolemy's catalogue number, as were many of Bayer's numbers) and designation "Decima septima", which means in Latin "The seventeenth". The meaning of this: Bayer designated 21 stars in the northern part of Eridanus along the river from east to west from the first (β, "Supra pedem Orionis in flumine, prima", that is "Above the foot of Orion in the river, the first") to the twenty-first (σ, "Vigesima prima", that is "the twenty-first"), and Epsilon Eridani was the seventeenth of them. These 21 stars are: β, λ, ψ, b, ω, μ, c, ν, ξ, ο (two stars), d, A, γ, π, δ, ε, ζ, ρ, η, σ. Bayer assigned Epsilon Eridani magnitude 3.
In 1690 Epsilon Eridani was included in the star catalogue of Johannes Hevelius. Its sequence number in constellation Eridanus was 14, its designation was "Tertia" ("the third"), and it was assigned magnitude 3 (according to Verbunt and Gent) or 4 (according to Baily). The star catalogue of English astronomer John Flamsteed, published in 1712, gave Epsilon Eridani the Flamsteed designation 18 Eridani because it was the eighteenth catalogued star in the constellation of Eridanus by order of increasing right ascension. In 1818 Epsilon Eridani was included in Friedrich Bessel's catalogue, based on James Bradley's observations during 1750–1762. Assigned magnitude was 4. It also appeared in Nicolas Louis de Lacaille's catalogue of 398 principal stars, whose 307-star version was published in 1755 in the Ephémérides des Mouvemens Célestes, pour dix années, 1755—1765, and whose full version was published in 1757 in Astronomiæ Fundamenta, Paris. In its 1831 edition by Francis Baily Epsilon Eridani has the number 50. Lacaille assigned it magnitude 3.
In 1801 Epsilon Eridani was included in Histoire Céleste Française, Joseph Jérôme Lefrançois de Lalande's catalogue of about 50,000 stars, based on his observations during 1791—1800, in which observations are arranged in a time order. It contains three observations of Epsilon Eridani: 1796 September 17 (page 246), 1796 December 3 (page 248) and 1797 November 13 (page 307). In 1847 an edition of Lalande's catalogue (Francis Baily et al.) was published, containing the majority of its observations, in which the stars were numbered in order of right ascension. Because every observation of every star was numbered and Epsilon Eridani was observed three times, it got three numbers: 6581, 6582 and 6583. (Today numbers from this catalogue are used with the prefix "Lalande", or "Lal"). Lalande assigned Epsilon Eridani magnitude 3. Also in 1801 it was included in the catalogue of Johann Bode, in which about 17,000 stars were grouped into 102 constellations and numbered (Epsilon Eridani got the number 159 in the constellation Eridanus). Bode's catalogue was based on observations of various astronomers, including Bode himself, but mostly on Lalande's and Lacaille's (for the southern sky), and an observer for Epsilon Eridani was Lalande. Bode assigned Epsilon Eridani magnitude 3. In 1814 Giuseppe Piazzi published the second edition of his star catalogue (its first edition was published in 1803), based on observations during 1792—1813, in which more than 7000 stars were grouped into 24 hours (0—23). Epsilon Eridani is number 89 in hour 3. Piazzi assigned it magnitude 4. In 1918 Epsilon Eridani appeared in the Henry Draper Catalogue with the designation HD 22049 and a preliminary spectral classification of K0.
Detection of proximity
Based on observations between 1800 and 1880, Epsilon Eridani was found to have a large proper motion across the celestial sphere, which was estimated at an angular velocity of three arcseconds annually. This movement implied it was relatively close to the Sun, making it a star of interest for the purpose of trigonometric parallax measurements. This process involves recording the position of Epsilon Eridani as the Earth moves around the Sun, which allows a star's distance to be estimated. From 1881 to 1883, American astronomer William L. Elkin used a heliometer at the Royal Observatory at the Cape of Good Hope, South Africa to compare the position of Epsilon Eridani with two nearby stars. From these observations, a parallax of 0.14 ± 0.02 arcseconds was calculated. By 1917, observers had refined their parallax estimate to 0.317 arcseconds. The modern value of 0.3109 arcseconds is equivalent to a distance of about 10.50 ly (3.22 parsecs).
Based on unexplained changes in the position of Epsilon Eridani between 1938 and 1972, Dutch–American astronomer Peter van de Kamp proposed that an unseen companion with an orbital period of 25 years was causing gravitational perturbations in its position. This claim was refuted in 1993 by German astronomer Wulff-Dieter Heintz and the false detection was blamed on a systematic error in the photographic plates.
Launched in 1983, the space telescope IRAS detected infrared emissions from stars near to the Sun. Two years later, the presence of an excess infrared emission close to Epsilon Eridani was announced, which indicated a disk of fine-grained cosmic dust was orbiting Epsilon Eridani. This debris disk has since been extensively studied. Evidence for a planetary system was discovered in 1998 by the observation of asymmetries in this dust ring. These clumps of dust could be explained by gravitational interaction with a planet orbiting just inside the ring of dust.
From 1980 to 2000, a team of astronomers led by American Artie P. Hatzes made radial velocity observations of Epsilon Eridani, measuring changes in motion of Epsilon Eridani along the line of sight to the Earth, which provided evidence of the gravitational effect of a planet orbiting it with a period of about seven years. Although there is a high level of noise in the radial velocity data due to magnetic activity in its photosphere, any periodicity caused by this magnetic activity is expected to show a strong correlation with variations in emission lines of ionized calcium (the Ca II H and K lines). Because no such correlation was found, a planetary companion was deemed the most likely cause. This discovery was supported by astrometric measurements of Epsilon Eridani made between 2001 and 2003 with the Hubble Space Telescope, which showed evidence for gravitational perturbation of Epsilon Eridani by a planet.
American astrophysicist Alice C. Quillen and her student Stephen Thorndike performed computer simulations of the structure of the dust disk around Epsilon Eridani. Their model suggested that the clumping of the dust particles could be explained by the presence of a second planet in an eccentric orbit. They announced this finding in 2002.
SETI and proposed exploration
In 1960, American physicist Philip Morrison and Italian physicist Giuseppe Cocconi proposed that extraterrestrial civilizations might be using radio signals for communication. Project Ozma, headed by American astronomer Frank Drake, used the Tatel Telescope to search for such signals from the nearby Sun-like stars Epsilon Eridani and Tau Ceti. The systems were observed at the emission frequency of neutral hydrogen, 1,420 MHz. No signals of intelligent extraterrestrial origin were detected. Drake repeated the experiment in 2010, with the same negative result. Despite this lack of success, Epsilon Eridani made its way into science fiction literature and television shows for many years following news of Drake's initial experiment.
In Habitable Planets for Man, a 1964 RAND Corporation study by American space scientist Stephen H. Dole, the odds of a habitable planet being in orbit around Epsilon Eridani were estimated at 3.3%. Among the known stars within 22 ly, it was listed with the 14 stars that were thought most likely to have a habitable planet.
American space scientist William I. McLaughlin proposed a new strategy in the search for extraterrestrial intelligence (SETI) in 1977. He suggested that widely observable events such as nova explosions might be used by intelligent extraterrestrials to synchronize the transmission and reception of their signals. This idea was tested from the National Radio Astronomy Observatory in 1988, which used outbursts of Nova Cygni 1975 as the timer. Fifteen days of observation showed no anomalous radio signals coming from Epsilon Eridani.
Because of the proximity and Sun-like properties of Epsilon Eridani, American physicist Robert L. Forward considered the system as one of the targets for interstellar travel in 1985. The following year, the British Interplanetary Society suggested Epsilon Eridani as one of several targets in its Project Daedalus paper study. The system has continued to be among the targets of such proposals, as with Project Icarus in 2011.
Based on its location within 23.5 ly (7.2 parsecs), Epsilon Eridani was among the target stars of Project Phoenix, a 1995 microwave survey for signals from extraterrestrial intelligence. The project had checked about 800 stars by 2004, but had not yet detected an unimpeachable signal.
Epsilon Eridani distance estimates
|Source||Parallax, mas||Distance, pc||Distance, ly||Distance, Pm||Ref.|
|Woolley et al. (1970)||302 ± 3||3.31 ± 0.03||10.8 ± 0.11||102.2 ± 1|||
|Gliese & Jahreiß (1991)||305.6 ± 2.6||3.272 ± 0.028||10.67 ± 0.09||101 ± 0.9|||
|van Altena et al. (1995)||304.9 ± 2.2||3.28+0.024
|10.7 ± 0.08||101.2 ± 0.7|||
|Perryman et al. (1997)
|310.75 ± 0.85||3.218 ± 0.009||10.496 ± 0.029||99.3 ± 0.27|||
|Perryman et al. (1997)
|322.6 ± 8.6||3.1 ± 0.08||10.11+0.28
|Benedict et al. (2006) (Section 6)||311.37 ± 0.1||3.2116 ± 0.001||10.475 ± 0.003||99.1 ± 0.03|||
|Benedict et al. (2006) (Table 10)||311.37 ± 0.11||3.2116 ± 0.0011||10.475 ± 0.004||99.1+0.04
|van Leeuwen (2007)||310.94 ± 0.16||3.2161 ± 0.0017||10.489 ± 0.005||99.24 ± 0.05|||
|RECONS TOP100 (2012)||311.22 ± 0.09[note 1]||3.2132 ± 0.0009||10.4799 ± 0.003||99.148 ± 0.029|||
Non-trigonometric distance estimates are marked in italic. The best estimate is marked in bold.
At a distance of 10.50 ly (3.22 parsecs), Epsilon Eridani is the 13th-nearest known star (and ninth nearest solitary star or stellar system) to the Sun as of 2014. Its proximity makes it one of the most studied stars of its stellar classification. Epsilon Eridani is located in the northern part of the constellation Eridanus, about 3° east of the slightly brighter star Delta Eridani. With a declination of −9.46°, Epsilon Eridani can be viewed from much of the Earth's surface. Only to the north of latitude 80° N is it permanently hidden below the horizon. The apparent magnitude of 3.73 can make it difficult to observe from an urban area with the unaided eye, because the night skies over cities are obscured by light pollution.
Epsilon Eridani has an estimated 82% of the Sun's mass and 74% of the Sun's radius, but only 34% of its luminosity. The estimated surface temperature is 5,084 K. With a stellar classification of K2 V, it is the second-nearest K-type main-sequence star after Alpha Centauri B. Indeed, since 1943, the spectrum of Epsilon Eridani has served as one of the stable anchor points by which other stars are classified. Its metallicity, or enrichment in elements heavier than helium, is slightly lower than the Sun's. In Epsilon Eridani's chromosphere, a region of the outer atmosphere just above the light emitting photosphere, the proportion of iron is estimated at 74% of the Sun's abundance.
Epsilon Eridani's K-type classification indicates that the spectrum has relatively weak absorption lines from energy absorbed by hydrogen and strong lines of neutral atoms and singly ionized calcium (Ca II). The luminosity class V is assigned to stars that are undergoing thermonuclear fusion of hydrogen in their core. For a K-type main-sequence star, this fusion is dominated by the proton–proton chain reaction, wherein a series of mergers of four hydrogen nuclei results in a helium nucleus. In their inner region, energy is transported outward from the core by means of radiation, which results in no net motion of the surrounding plasma. Outside of this region, in their envelope, energy is carried to the photosphere by plasma convection, where it then radiates into space.
Epsilon Eridani has a higher level of magnetic activity than the Sun, and hence demonstrates increased activity in the outer parts of its atmosphere: the chromosphere and corona. The average magnetic-field strength of Epsilon Eridani across the entire surface is (1.65 ± 0.30) × 10−2 T, which is more than forty times greater than the (5–40) × 10−5 T magnetic field strength in the Sun's photosphere. The magnetic properties can be modeled by assuming that regions with a magnetic flux of about 0.14 T randomly cover approximately 9% of the photosphere, whereas the remainder of the surface is free of magnetic fields. The overall magnetic activity of Epsilon Eridani is irregular, but it may vary with a 4.9-year period. Assuming that its radius does not change over this interval, the long-term variation in activity level appears to produce a temperature variation of 15 K, which corresponds to a variation in visual magnitude (V) of 0.014.
The magnetic field on the surface of Epsilon Eridani causes variations in the hydrodynamic behavior of the photosphere. This results in greater jitter during measurements of its radial velocity Doppler shift. Variations of 15 m s−1 were measured over a 20 year period, which is much higher than the measurement error rate of 3 m s−1. This makes interpretation of periodicities in the radial velocity of Epsilon Eridani, such as those caused by the gravitational perturbations of an orbiting planet, more difficult.
Epsilon Eridani is classified as a BY Draconis variable because it has regions of higher magnetic activity that move into and out of the line of sight as it rotates. Measurement of this rotational modulation suggests that its equatorial region rotates with an average period of 11.2 days, which is less than half of the rotation period of the Sun. Observations have shown that Epsilon Eridani varies as much as 0.050 in V magnitude due to starspots and other short-term magnetic activity. Photometry has also shown that the surface of Epsilon Eridani, like the Sun, is undergoing differential rotation, which means that the rotation period at the surface varies by latitude. The measured periods range from 10.8 to 12.3 days.[note 2] The axial tilt of Epsilon Eridani toward the line of sight from Earth is uncertain. Estimates range from 24° to 72°.
The high levels of chromospheric activity, strong magnetic field, and relatively fast rotation rate of Epsilon Eridani are characteristic of a young star. The age of Epsilon Eridani is about 440 million years, but this remains subject to debate. Most age estimation methods place it in the range from 200 million to 800 million years. However, the low abundance of heavy elements in the chromosphere of Epsilon Eridani is indicative of an older star, because the medium out of which stars form is steadily enriched by heavier elements produced by older generations of stars. This anomaly might be caused by a diffusion process that has transported some of the helium and heavier elements out of the photosphere and into a region below Epsilon Eridani's convection zone.
The X-ray luminosity of Epsilon Eridani is about 2 × 1028 ergs/s (2 × 1021 W). It is brighter in X-ray emission than the Sun at peak activity. The source for this strong X-ray emission is Epsilon Eridani's hot corona. Epsilon Eridani's corona appears larger and hotter than the Sun's, with a temperature of 3.4 × 106 K as measured from observation of the corona's ultraviolet and X-ray emission.
The stellar wind emitted by Epsilon Eridani expands until it collides with the surrounding interstellar medium of sparse gas and dust, resulting in a bubble of heated hydrogen gas. The absorption spectrum from this gas has been measured with the Hubble Space Telescope, allowing the properties of the stellar wind to be estimated. Epsilon Eridani's hot corona results in a mass loss rate from Epsilon Eridani's stellar wind that is 30 times higher than the Sun's. This wind is generating an astrosphere (the equivalent of the heliosphere that surrounds the Sun) that spans about 8,000 AU and contains a bow shock that lies 1,600 AU from Epsilon Eridani. At its estimated distance from Earth, this astrosphere spans 42 arcminutes, which is wider than the apparent size of the full Moon.
Epsilon Eridani has a high proper motion, moving −0.976 arcseconds per year in right ascension (the celestial longitude) and 0.018 arcseconds per year in declination (the celestial latitude), for a total proper motion of 0.962 arcseconds per year.[note 3] It has a radial velocity of +15.5 km/s away from the Sun. The space velocity components of Epsilon Eridani in the galactic coordinate system are (U, V, W) = (−3, +7, −20) km/s, which means that it is traveling within the Milky Way at a mean galactocentric distance of 28.7 kly (8.79 kiloparsecs) from the core along an orbit that has an eccentricity of 0.09. The velocity and heading of Epsilon Eridani indicate that it may be a member of the Ursa Major Moving Group that share a common motion through space. This behavior suggests that the members originated in an open cluster that has since diffused. The estimated age of this group is 500±100 million years, which lies within the range of the age estimates for Epsilon Eridani.
During the past million years, three stars are believed to have come within 7 ly (2 parsecs) of Epsilon Eridani. The most recent and closest of these encounters was with Kapteyn's Star, which approached to a distance of about 3 ly (0.9 parsecs) roughly 12,500 years ago. The other two stars were Sirius and Ross 614. None of these encounters are thought to have affected the circumstellar disk orbiting Epsilon Eridani.
Epsilon Eridani made its closest approach to the Sun about 105,000 years ago, when they were separated by 7 ly (2.1 parsecs). Based upon a simulation of close encounters with nearby stars, the binary star system Luyten 726-8, which includes the variable star UV Ceti, will encounter Epsilon Eridani in approximately 31,500 years at a minimum distance of about 0.9 ly (0.29 parsecs). They will be less than 1 ly (0.3 parsecs) apart for about 4,600 years. If Epsilon Eridani has an Oort cloud, Luyten 726-8 could gravitationally perturb some of the comets with long orbital periods.
(in order from star)
|Asteroid belt||3 AU||—||—|
|b (unconfirmed)||1.55 ± 0.24 MJ||3.38–3.50||2,502–2,630||0.25–0.702||—||—|
|Asteroid belt||20 AU||—||—|
|c (unconfirmed)||0.1 MJ||40?||102,270||0.3||—||—|
|Dust disk||35–100 AU||—||—|
Observations with the James Clerk Maxwell Telescope at a wavelength of 850 μm show an extended flux of radiation out to an angular radius of 35 arcseconds around Epsilon Eridani. The peak emission occurs at an angular radius of 18 arcseconds, which corresponds to a radius of about 60 AU. The highest level of emission occurs over the radius 35–75 AU from Epsilon Eridani and is substantially reduced inside 30 AU. This emission is interpreted as coming from a young analogue of the Solar System's Kuiper belt: a compact dusty disk structure surrounding Epsilon Eridani. From Earth, this belt is viewed at an inclination of roughly 25° to the line of sight.
Dust and possibly water ice from this belt migrates inward because of drag from the stellar wind and a process by which stellar radiation causes dust grains to slowly spiral toward Epsilon Eridani, known as the Poynting–Robertson effect. At the same time, these dust particles can be destroyed through mutual collisions. The time scale for all of the dust in the disk to be cleared away by these processes is less than Epsilon Eridani's estimated age. Hence, the current dust disk must have been created by collisions or other effects of larger parent bodies, and the disk represents a late stage in the planet-formation process. It would have required collisions between 11 Earth masses' worth of parent bodies to have maintained the disk in its current state over its estimated age.
The disk contains an estimated mass of dust equal to a sixth of the mass of the Moon, with individual dust grains exceeding 3.5 μm in size at a temperature of about 55 K. This dust is being generated by the collision of comets, which range up to 10 to 30 km in diameter and have a combined mass of 5 to 9 times that of Earth. This is similar to the estimated 10 Earth masses in the primordial Kuiper belt. However, the disk around Epsilon Eridani contains less than 2.2 × 1017 kg of carbon monoxide. This low level suggests a paucity of volatile-bearing comets and icy planetesimals compared to the Kuiper belt.
The clumpy structure of the dust belt may be explained by gravitational perturbation from a planet, dubbed Epsilon Eridani b. The clumps in the dust occur at orbits that have an integer resonance with the orbit of the suspected planet. For example, the region of the disk that completes two orbits for every three orbits of a planet is in a 3:2 orbital resonance. In computer simulations the ring morphology can be reproduced by the capture of dust particles in 5:3 and 3:2 orbital resonances with a planet that has an orbital eccentricity of about 0.3. Alternatively, the clumpiness may have been caused by collisions between minor planets known as plutinos.
Observations from NASA's Spitzer Space Telescope suggest that Epsilon Eridani actually has two asteroid belts and a cloud of exozodiacal dust. The latter is an analog of the zodiacal dust that occupies the plane of the Solar System. One belt sits at approximately the same position as the one in the Solar System, orbiting at a distance of 3.00 ± 0.75 AU from Epsilon Eridani, and consists of silicate grains with a diameter of 3 μm and a combined mass of about 1018 kg. If the planet Epsilon Eridani b exists then this belt is unlikely to have had a source outside the orbit of the planet, so the dust may have been created by fragmentation and cratering of larger bodies such as asteroids. The second, denser belt, most likely also populated by asteroids, lies between the first belt and the outer comet disk. The structure of the belts and the dust disk suggests that more than two planets in the Epsilon Eridani system are needed to maintain this configuration.
In an alternative scenario, the exozodiacal dust may be generated in an outer belt, which is orbiting between 55 and 90 AU from Epsilon Eridani and has an assumed mass of 10−3 times the mass of the Earth. This dust is then transported inward past the orbit of Epsilon Eridani b. When collisions between the dust grains are taken into account, the dust will reproduce the observed infrared spectrum and brightness. Outside the radius of ice sublimation, located beyond 10 AU from Epsilon Eridani where the temperatures fall below 100 K, the best fit to the observations occurs when a mix of ice and silicate dust is assumed. Inside this radius, the dust must consist of silicate grains that lack volatiles.
The inner region around Epsilon Eridani, from a radius of 2.5 AU inward, appears to be clear of dust down to the detection limit of the 6.5 m MMT telescope. Grains of dust in this region are efficiently removed by drag from the stellar wind, while the presence of a planetary system may also help keep this area clear of debris. Still, this does not preclude the possibility that an inner asteroid belt may be present with a combined mass no greater than the asteroid belt in the Solar System.
As one of the nearest Sun-like stars, Epsilon Eridani has been the target of many attempts to search for planetary companions. However, its chromospheric activity and variability means that finding planets with the radial velocity method is difficult, because the stellar activity may create signals that mimic the presence of planets. Attempts at direct imaging of potential exoplanets have proven unsuccessful to date. Infrared observation has shown there are no bodies of three or more Jupiter masses in this system.
Referred to as Epsilon Eridani b, this planet was announced in 2000, but the discovery has remained controversial. A comprehensive study in 2008 called the detection "tentative" and described the proposed planet as "long suspected but still unconfirmed". However, many astronomers believe the evidence is sufficiently compelling that they regard the discovery as confirmed.
Published sources remain in disagreement as to the proposed planet's basic parameters. Values for its orbital period range from 6.85 to 7.2 years. Estimates of the mean radius of its elliptical orbit—the semimajor axis—range from 3.38 AU to 3.50 AU and approximations of its orbital eccentricity range from 0.25 ± 0.23 to 0.702 ± 0.039.
The true mass of this planet remains unknown, but it can be estimated based on the displacement effect of the planet's gravity on Epsilon Eridani. Only the component of the displacement along the line of sight to the Earth is known, which yields a value for the formula m sin i, where m is the mass of the planet and i is the orbital inclination. Estimates for the value of m sin i range from 0.60 Jupiter masses to 1.06 Jupiter masses, which sets the lower limit for the mass of the planet (because the sine function has a maximum value of 1). By choosing a mass of 0.78 and an estimated inclination of 30°, this yields the frequently cited value of 1.55 ± 0.24 Jupiter masses for the planet's mass.
Of all the measured parameters for this planet, the value for orbital eccentricity is the most uncertain. The frequently cited value of 0.7 for Epsilon Eridani b's eccentricity is inconsistent with the presence of the proposed asteroid belt at a distance of 3 AU. If the eccentricity was actually this high, the planet would pass through the asteroid belt and clear it out within about ten thousand years. If the belt has existed for longer than this period, which appears likely, it imposes an upper limit on Epsilon Eridani b's eccentricity of about 0.10–0.15. If the dust disk is instead being generated from the outer debris disk, rather than from collisions in an asteroid belt, then no constraints on the planet's orbital eccentricity are needed to explain the dust distribution.
Computer simulations of the dusty disk orbiting Epsilon Eridani suggest that the shape of the disk may be explained by the presence of a second planet, tentatively dubbed Epsilon Eridani c. Clumping in the dust disk may occur because dust particles are being trapped in orbits that have resonant orbital periods with a planet in an eccentric orbit. The postulated Epsilon Eridani c would orbit at a distance of 40 AU, with an eccentricity of 0.3 and a period of 280 years. The inner cavity of the disk may be explained by the presence of additional planets. Current models of planet formation cannot easily explain how a planet could have been created at this distance from Epsilon Eridani. The disk is expected to have dissipated long before a giant planet could have formed. Instead, the planet may have formed at an orbital distance of about 10 AU then migrated outward because of gravitational interaction with the disc or with other planets in the system.
Epsilon Eridani is a target for planet finding programs because it has properties that allow an Earth-like planet to form. Although this system was not chosen as a primary candidate for the now-canceled Terrestrial Planet Finder, it was a target star for NASA's proposed Space Interferometry Mission to search for Earth-sized planets. The proximity, Sun-like properties and suspected planets of Epsilon Eridani have also made it the subject of multiple studies on whether an interstellar probe can be sent to Epsilon Eridani.
The orbital radius at which the stellar flux from Epsilon Eridani matches the solar constant—where the emission matches the Sun's output at the orbital distance of the Earth—is 0.61 astronomical units (AU). That is within the maximum habitable zone of a conjectured Earth-like planet orbiting Epsilon Eridani, which currently stretches from about 0.5 to 1.0 AU. As Epsilon Eridani ages over a period of 20 billion years, the net luminosity will increase, causing this zone to slowly expand outward to about 0.6–1.4 AU. However, the presence of a large planet with a highly elliptical orbit in proximity to Epsilon Eridani's habitable zone reduces the likelihood of a terrestrial planet having a stable orbit within the habitable zone.
A young star such as Epsilon Eridani can produce large amounts of ultraviolet radiation that may be harmful to life. The orbital radius where the UV flux matches that on the early Earth lies at just under 0.5 AU. Epsilon Eridani's proximity, Sun-like properties and suspected planets have made it a destination for interstellar travel in science fiction stories.
- Epsilon Eridani in fiction
- List of exoplanetary host stars
- List of extrasolar planets
- List of nearest stars
Notes and references
- Weighted parallax based on parallaxes from van Altena et al. (1995), Benedict et al. (2006) and van Leeuwen (2007).
- The rotation period Pβ at latitude β is given by:
- Pβ = Peq/(1 − k sin β)
- 0.03 ≤ k ≤ 0.10
- The total proper motion μ can be computed from:
- μ2 = (μα cos δ)2 + μδ2
- μ2 = (−975.17 · cos(−9.458°))2 + 19.492 = 925658.1
- van Leeuwen, Floor (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, arXiv:0708.1752v1, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. Note: see VizieR catalogue I/311.
- Cousins, A. W. J. (1984), "Standardization of Broadband Photometry of Equatorial Standards", South African Astronomical Observatory Circulars 8: 59, Bibcode:1984SAAOC...8...59C.
- Gray, R. O. et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample", The Astronomical Journal 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637.
- "V* eps Eri – variable of BY Dra type", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2010-11-05.
- Cutri, R. M. et al. (June 2003), "The IRSA 2MASS all-sky point source catalog, NASA/IPAC infrared science archive", The IRSA 2MASS All-Sky Point Source Catalog, Bibcode:2003tmc..book.....C.
- "GCVS query=eps Eri", General Catalog of Variable Stars (Sternberg Astronomical Institute, Moscow, Russia), retrieved 2009-05-20.
- Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick, ed., "The revision of the general catalogue of radial velocities", Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30 (University of Toronto: International Astronomical Union) 30: 57, Bibcode:1967IAUS...30...57E.
- Benedict, G. Fritz et al. (November 2006), "The extrasolar planet e Eridani b – orbit and mass", The Astronomical Journal 132 (5): 2206–2218, arXiv:astro-ph/0610247, Bibcode:2006AJ....132.2206B, doi:10.1086/508323.
- Staff (June 8, 2007), The one hundred nearest star systems, Research Consortium On Nearby Stars, retrieved 2007-11-29
- Gonzalez, G.; Carlson, M. K.; Tobin, R. W. (April 2010), "Parent stars of extrasolar planets – X. Lithium abundances and v sini revisited", Monthly Notices of the Royal Astronomical Society 403 (3): 1368–1380, arXiv:0912.1621, Bibcode:2010MNRAS.403.1368G, doi:10.1111/j.1365-2966.2009.16195.x. See table 3.
- Baines, Ellyn K.; Armstrong, J. Thomas (2011), "Confirming Fundamental Parameters of the Exoplanet Host Star epsilon Eridani Using the Navy Optical Interferometer", The Astrophysical Journal, arXiv:1112.0447, Bibcode:2012ApJ...748...72B, doi:10.1088/0004-637X/748/1/72
- Demory, B.-O. et al. (October 2009), "Mass-radius relation of low and very low-mass stars revisited with the VLTI", Astronomy and Astrophysics 505 (1): 205–215, arXiv:0906.0602, Bibcode:2009A&A...505..205D, doi:10.1051/0004-6361/200911976. See Table B.1
- Saumon, D. et al. (April 1996), "A theory of extrasolar giant planets", The Astrophysical Journal 460: 993, arXiv:astro-ph/9510046, Bibcode:1996ApJ...460..993S, doi:10.1086/177027. See Table A1, p. 21.
- Kovtyukh, V. V. et al. (December 2003), "High precision effective temperatures for 181 F-K dwarfs from line-depth ratios", Astronomy and Astrophysics 411 (3): 559–564, arXiv:astro-ph/0308429, Bibcode:2003A&A...411..559K, doi:10.1051/0004-6361:20031378.
- Santos, N. C.; Israelian, G.; Mayor, M. (March 2004), "Spectroscopic [Fe/H] for 98 extra-solar planet-host stars: Exploring the probability of planet formation", Astronomy and Astrophysics 415 (3): 1153–1166, arXiv:astro-ph/0311541, Bibcode:2004A&A...415.1153S, doi:10.1051/0004-6361:20034469.—the percentage of iron is given by , or 74%
- Fröhlich, H.-E. (December 2007), "The differential rotation of Epsilon Eri from MOST data", Astronomische Nachrichten 328 (10): 1037–1039, arXiv:0711.0806, Bibcode:2007AN....328.1037F, doi:10.1002/asna.200710876.
- Janson, M. et al. (September 2008), "A comprehensive examination of the ε Eridani system. Verification of a 4 micron narrow-band high-contrast imaging approach for planet searches", Astronomy and Astrophysics 488 (2): 771–780, arXiv:0807.0301, Bibcode:2008A&A...488..771J, doi:10.1051/0004-6361:200809984.
- Di Folco, E. et al. (November 2004), "VLTI near-IR interferometric observations of Vega-like stars. Radius and age of α PsA, β Leo, β Pic, ε Eri and τ Cet", Astronomy and Astrophysics 426 (2): 601–617, Bibcode:2004A&A...426..601D, doi:10.1051/0004-6361:20047189.
- Hatzes, Artie P. et al. (December 2000), "Evidence for a long-period planet orbiting ε Eridani", The Astrophysical Journal 544 (2): L145–L148, arXiv:astro-ph/0009423, Bibcode:2000ApJ...544L.145H, doi:10.1086/317319.
- Schneider, Jean, "Star: Eps Eridani", Extrasolar Planets Encyclopaedia (Paris Observatory), retrieved 2010-07-04.
- Buccino, A. P.; Mauas, P. J. D.; Lemarchand, G. A. (June 2003), R. Norris and F. Stootman, ed., "UV Radiation in Different Stellar Systems", Bioastronomy 2002: Life Among the Stars, Proceedings of IAU Symposium #213 (San Francisco: Astronomical Society of the Pacific) 213: 97, Bibcode:2004IAUS..213...97B.
- Aguilar, David A.; Pulliam, Christine (October 27, 2008), Solar System's young twin has two asteroid belts, Harvard-Smithsonian Center for Astrophysics, retrieved 2008-11-10.
- Backman, D. et al. (2008), "Epsilon Eridani's planetary debris disk: structure and dynamics based on Spitzer and CSO observations", The Astrophysical Journal 690 (2): 1522–1538, arXiv:0810.4564, Bibcode:2009ApJ...690.1522B, doi:10.1088/0004-637X/690/2/1522.
- Potemine, Igor Yu. (April 12, 2010). "Transit of Luyten 726-8 within 1 ly from Epsilon Eridani". arXiv:1004.1557 [astro-ph.SR]. Bibcode 2010arXiv1004.1557P.
- Villard, Ray (December 2007), "Does life exist on this exoplanet?", Astronomy 35 (12): 44–47, Bibcode:2007Ast....35l..44V.
- Boyle, Alan (2009), "The case for Pluto: how a little planet made a big difference", The Case for Pluto: How a Little Planet Made a Big Difference by Alan Boyle. Wiley (Hoboken, New Jersey: John Wiley and Sons): 191, Bibcode:2009cphl.book.....B, ISBN 0-470-50544-3.
- Baily, Francis (1843). "The Catalogues of Ptolemy, Ulugh Beigh, Tycho Brahe, Halley, Hevelius, Deduced from the Best Authorities. With Various Notes and Corrections, and a Preface to Each Catalogue. To Which is Added the Synonym of each Star, in the Catalogues of Flamsteed of Lacaille, as far as the same can be ascertained". Memoirs of the Royal Astronomical Society 13: 1. Bibcode:1843MmRAS..13....1B. (Epsilon Eridani: for Ptolemy's catalogue see page 60, for Ulugh Beg's – page 109, for Tycho Brahe's – page 156, for Hevelius' – page 209).
- Verbunt, F.; van Gent, R. H. (2012). "The star catalogues of Ptolemaios and Ulugh Beg. Machine-readable versions and comparison with the modern Hipparcos Catalogue". Astronomy & Astrophysics 544: A31. arXiv:1206.0628. Bibcode:2012A&A...544A..31V. doi:10.1051/0004-6361/201219596.
- Звёздный каталог ал-Бируни с приложением каталогов Хайяма и ат-Туси. djvu. (Epsilon Eridani: see page 135).
- Verbunt, F.; van Gent, R. H. (2010). "Three editions of the star catalogue of Tycho Brahe. Machine-readable versions and comparison with the modern Hipparcos Catalogue". Astronomy & Astrophysics 516: A28. Bibcode:2010A&A...516A..28V. doi:10.1051/0004-6361/201014002.
- Swerdlow, N. M. (August 1986), "A star catalogue used by Johannes Bayer", Journal for the History of Astronomy 17 (50): 189–197, Bibcode:1986JHA....17..189S. See p. 192.
- Hoffleit, D.; Warren Jr., W. H. (1991), Bright star catalogue (5th ed.), Yale University Observatory, retrieved 2010-07-05.
- Bayer, Johann (1603). "Uranometria: omnium asterismorum continens schemata, nova methodo delineata, aereis laminis expressa". Uranometria in Linda Hall Library: link. Pages on constellation Eridanus: Table, Map.
- Verbunt, F.; van Gent, R. H. (2010). "The star catalogue of Hevelius. Machine-readable version and comparison with the modern Hipparcos Catalogue". Astronomy & Astrophysics 516: A29. Bibcode:2010A&A...516A..29V. doi:10.1051/0004-6361/201014003.
- Bessel, Friedrich Wilhelm (1818). "Fundamenta astronomiae pro anno MDCCLV deducta ex observationibus viri incomparabilis James Bradley in specula astronomica Grenovicensi per annos 1750-1762 institutis". Frid. Nicolovius. Google Books id: UHRYAAAAcAAJ. Page with Epsilon Eridani: 158.
- Lacaille, Nicolas Louis de. (1755). "Ephemerides des mouvemens celestes, pour dix années, depuis 1755 jusqu'en 1765, et pour le meridien de la ville de Paris". Paris. Google Books id: CGHtdxdcc5UC. (Epsilon Eridani: see page LV of the "Introduction").
- Lacaille, Nicolas Louis de. (1757). "Astronomiæ fundamenta". Paris. Google Books id: -VQ_AAAAcAAJ. (Epsilon Eridani: see page 233 (in the catalogue), see also pages 96, 153—154, 189, 231).
- Baily, Francis (1831). "On Lacaille's catalogue of 398 stars". Monthly Notices of the Royal Astronomical Society 2: 33. Bibcode:1831MNRAS...2...33B. doi:10.1093/mnras/2.5.33. (Epsilon Eridani: see page 110).
- Lalande, Joseph Jérôme Le Français de (1801). "Histoire Céleste Française". Paris, Imprimerie de la République. Google Books id: f9AMAAAAYAAJ. Pages with Epsilon Eridani: 246, 248, 307.
- Baily, Francis; Lalande, Joseph Jérôme Le Français de (1847). "Catalogue of those stars in the Histoire Celeste Francaise of Jerome Delalande, for which tables of reduction to the epoch 1800 habe been published by Prof. Schumacher". London (1847). Bibcode:1847cshc.book.....B. Google Books id: oc0-AAAAcAAJ. Page with Epsilon Eridani: 165.
- Dictionary of Nomenclature of Celestial Objects. Lal entry. SIMBAD. Centre de Données astronomiques de Strasbourg.
- Bode, Johann Elert (1801). "Algemaine Beschreibung u. Nachweisung der gestine nebst Verzeichniss der gerarden Aufsteigung u. Abweichung von 17240 Sternen Doppelsternen Nobelflocken u. Sternhaufen". Berlin: Beym Verfasser. Bibcode:1801abun.book.....B. Google Books id: NUlRAAAAcAAJ. (List of observers and description of the catalogue: see page 32 of the "Introduction". List of constellations: see page 96). (Epsilon Eridani: see page 71).
- Piazzi, Giuseppe. (1814). "Praecipuaram stellarum inerranthium positiones mediae ineunte saeculo 19. EX observationibus habilis in specula panormitana AB anno 1792 AD annum 1813". Palermo: Tip. Militare. Bibcode:1814psip.book.....P. Google Books id: c40RAAAAYAAJ. (Epsilon Eridani: see page 22).
- Cannon, Annie J.; Pickering, Edward C. (1918), "The Henry Draper catalogue 0h, 1h, 2h, and 3h", Annals of Harvard College Observatory 91: 1–290, Bibcode:1918AnHar..91....1C.—see p. 236
- Gill, David; Elkin, W. L. (1884), Heliometer determinations of stellar parallaxes in the southern hemisphere, London, U.K.: The Royal Astronomical Society, pp. 174–180.
- Belkora, Leila (2002), Minding the heavens: the story of our discovery of the Milky Way, London, U.K.: CRC Press, p. 151, ISBN 0-7503-0730-7.
- Gill, David (1893), Heliometer observations for determination of stellar parallax, London: Eyre and Spottiswoode, p. xvi.
- Gill, David (1884), "The fixed stars", Nature 30 (763): 156–159, Bibcode:1884Natur..30..156., doi:10.1038/030156a0.
- Adams, W. S.; Joy, A. H. (1917), "The luminosities and parallaxes of five hundred stars", The Astrophysical Journal 46: 313–339, Bibcode:1917ApJ....46..313A, doi:10.1086/142369.
- van de Kamp, P. (April 1974), "Parallax and orbital motion of Epsilon Eridani", The Astronomical Journal 79: 491–492, Bibcode:1974AJ.....79..491V, doi:10.1086/111571.
- Heintz, W. D. (March 1992), "Photographic astrometry of binary and proper-motion stars. VII", The Astronomical Journal 105 (3): 1188–1195, Bibcode:1993AJ....105.1188H, doi:10.1086/116503. See the note for BD -9°697 on page 1192.
- Neugebauer, G. et al. (March 1984), "The Infrared Astronomical Satellite (IRAS) mission", The Astrophysical Journal 278: L1–L6, Bibcode:1984ApJ...278L...1N, doi:10.1086/184209.
- Aumann, H. H. (October 1985), "IRAS observations of matter around nearby stars", Publications of the Astronomical Society of the Pacific 97: 885–891, Bibcode:1985PASP...97..885A, doi:10.1086/131620.
- Greaves, J. S. et al. (October 1998), "A dust ring around Epsilon Eridani: analog to the young Solar System", The Astrophysical Journal 506 (2): L133–L137, arXiv:astro-ph/9808224, Bibcode:1998ApJ...506L.133G, doi:10.1086/311652.
- Marcy, Geoffrey W. et al. (August 7–11, 2000), A. Penny, ed., "Planetary Messages in the Doppler Residuals (Invited Review)", Planetary Systems in the Universe, Proceedings of IAU Symposium #202 (Manchester, United Kingdom) 202: 20–28, Bibcode:2004IAUS..202...20M.
- Janson, Markus et al. (June 2007), "NACO-SDI Direct Imaging Search for the Exoplanet ε Eri b", The Astronomical Journal 133 (6): 2442–2456, arXiv:astro-ph/0703300, Bibcode:2007AJ....133.2442J, doi:10.1086/516632.
- Quillen, A. C.; Thorndike, Stephen (October 2002), "Structure in the ε Eridani dusty disk caused by mean motion resonances with a 0.3 eccentricity planet at periastron", The Astrophysical Journal 578 (2): L149–L142, arXiv:astro-ph/0208279, Bibcode:2002ApJ...578L.149Q, doi:10.1086/344708.
- Gugliucci, Nicole (May 24, 2010), "Frank Drake returns to search for extraterrestrial life", Discovery News (Discovery Communications, LLC), retrieved 2010-07-05.
- Heidmann, Jean; Dunlop, Storm (1995), Extraterrestrial intelligence, Cambridge, U.K.: Cambridge University Press, p. 113, ISBN 0-521-58563-5.
- Marschall, Laurence A.; Maran, Stephen P. (2009), Pluto confidential: an insider account of the ongoing battles over the status of Pluto, BenBella Books, p. 171, ISBN 1-933771-80-1.
- Dole, Stephen H. (1964), Habitable planets for man (1st ed.), New York, N.Y.: Blaisdell Publishing Company, pp. 110 & 113, ISBN 0-444-00092-5, retrieved 2008-07-22.
- Forbes, M. A.; Westpfahl, D. J. (September 1988), "A test of McLaughlin's strategy for timing SETI experiments", Bulletin of the American Astronomical Society 20: 1043, Bibcode:1988BAAS...20.1043F.
- Forward, R. L. (May–June 1985), "Starwisp – an ultra-light interstellar probe", Journal of Spacecraft and Rockets 22 (3): 345–350, Bibcode:1985JSpRo..22..345F, doi:10.2514/3.25754.
- Martin, A. R. (February 1976), "Project Daedalus – The ranking of nearby stellar systems for exploration", Journal of the British Interplanetary Society 29: 94–100, Bibcode:1976JBIS...29...94M.
- Long, K. F.; Obousy, R. K.; Hein, A. (January 25, 2011), "Project Icarus: Optimisation of nuclear fusion propulsion for interstellar missions", Acta Astronautica 68 (11–12): 1820, Bibcode:2011AcAau..68.1820L, doi:10.1016/j.actaastro.2011.01.010.
- Duquennoy, A. et al. (August 16–20, 1993), "The current state of target selection for NASA's high resolution microwave survey", Progress in the Search for Extraterrestrial Life, Astronomical Society of the Pacific Conference Series 74, Santa Cruz, California: Astronomical Society of the Pacific, pp. 207–218, Bibcode:1995ASPC...74..207H.
- Whitehouse, David (March 25, 2004), Radio search for ET draws a blank, BBC News, retrieved 2008-07-22.
- Woolley R.; Epps E. A.; Penston M. J.; Pocock S. B. (1970). "Woolley 144". Catalogue of stars within 25 parsecs of the Sun. Retrieved 2014-09-28.
- Gliese, W. and Jahreiß, H. (1991). "Gl 144". Preliminary Version of the Third Catalogue of Nearby Stars. Retrieved 2014-09-28.
- Van Altena W. F., Lee J. T., Hoffleit E. D. (1995). "GCTP 742". The General Catalogue of Trigonometric Stellar Parallaxes, Fourth Edition. Retrieved 2014-09-28.
- Perryman et al. (1997). "HIP 16537". The Hipparcos and Tycho Catalogues. Retrieved 2014-09-28.
- Perryman et al. (1997). "HIP 16537". The Hipparcos and Tycho Catalogues. Retrieved 2014-09-28.
- van Leeuwen F. (2007). "HIP 16537". Validation of the new Hipparcos reduction. Retrieved 2014-09-28.
- "RECONS TOP100". THE ONE HUNDRED NEAREST STAR SYSTEMS brought to you by RECONS (Research Consortium On Nearby Stars). 2012. Retrieved 2014-09-28.
- Vieytes, Mariela C.; Mauas, Pablo J. D.; Díaz, Rodrigo F. (September 2009), "Chromospheric changes in K stars with activity", Monthly Notices of the Royal Astronomical Society 398 (3): 1495–1504, arXiv:0906.1760, Bibcode:2009MNRAS.398.1495V, doi:10.1111/j.1365-2966.2009.15207.x.
- Campbell, William Wallace (1899), The elements of practical astronomy, New York, N.Y.: The MacMillan Company, pp. 109–110.
- Narisada, Kohei; Schreuder, Duco (2004), "Light pollution handbook", Light pollution handbook (Dordrecht, The Netherlands: Springer) 322: 118–132, Bibcode:2004ASSL..322.....N, ISBN 1-4020-2665-X.
- Garrison, R. F. (December 1993), "Anchor Points for the MK System of Spectral Classification", Bulletin of the American Astronomical Society 25: 1319, Bibcode:1993AAS...183.1710G, retrieved 2012-02-04.
- Karttunen, Hannu; Oja, H. (2007), Fundamental astronomy (5th ed.), Heidelberg, Germany: Springer, pp. 209–213, 247–249, ISBN 3-540-34143-9.
- Rüedi, I.; Solanki, S. K.; Mathys, G.; Saar, S. H. (February 1997), "Magnetic field measurements on moderately active cool dwarfs", Astronomy and Astrophysics 318: 429–442, Bibcode:1997A&A...318..429R.
- Wang, Y.-M.; Sheeley, N. R., Jr. (July 2003), "Modeling the Sun's Large-Scale Magnetic Field during the Maunder Minimum", The Astrophysical Journal 591 (2): 1248–1256, Bibcode:2003ApJ...591.1248W, doi:10.1086/375449.
- Valenti, Jeff A.; Marcy, Geoffrey W.; Basri, Gibor (February 1995), "Infrared zeeman analysis of Epsilon Eridani", The Astrophysical Journal, Part 1 439 (2): 939–956, Bibcode:1995ApJ...439..939V, doi:10.1086/175231.
- Buccino, A. P.; Mauas, P. J. D. (June 2008), "Mg II h+k emission lines as stellar activity indicators of main sequence F-K stars", Astronomy and Astrophysics 483 (3): 903–910, arXiv:0804.1101, Bibcode:2008A&A...483..903B, doi:10.1051/0004-6361:20078925.
- Gray, David F.; Baliunas, Sallie L. (March 1995), "Magnetic activity variations of Epsilon Eridani", The Astrophysical Journal, Part 1 441 (1): 436–442, Bibcode:1995ApJ...441..436G, doi:10.1086/175368.
- Frey, Gary J. et al. (November 1991), "The rotation period of Epsilon Eri from photometry of its starspots", The Astrophysical Journal 102 (5): 1813–1815, Bibcode:1991AJ....102.1813F, doi:10.1086/116005.
- Drake, Jeremy J.; Smith, Geoffrey (August 1993), "The fundamental parameters of the chromospherically active K2 dwarf Epsilon Eridani", The Astrophysical Journal, Part 1 412 (2): 797–809, Bibcode:1993ApJ...412..797D, doi:10.1086/172962.
- Rocha-Pinto, H. J. et al. (June 2000), "Chemical enrichment and star formation in the Milky Way disk. I. Sample description and chromospheric age-metallicity relation", Astronomy and Astrophysics 358: 850–868, arXiv:astro-ph/0001382, Bibcode:2000A&A...358..850R.
- Gai, Ning; Bi, Shao-Lan; Tang, Yan-Ke (October 2008), "Modeling ε Eri and asteroseismic tests of element diffusion", Chinese Journal of Astronomy and Astrophysics 8 (5): 591–602, arXiv:0806.1811, Bibcode:2008ChJAA...8..591G, doi:10.1088/1009-9271/8/5/10.
- Johnson, H. M. (January 1, 1981), "An X-ray sampling of nearby stars", Astrophysical Journal, Part 1 243: 234–243, Bibcode:1981ApJ...243..234J, doi:10.1086/158589.
- Schmitt, J. H. M. M. et al. (February 1996), "The extreme-ultraviolet spectrum of the nearby K Dwarf ε Eridani", Astrophysical Journal 457: 882, Bibcode:1996ApJ...457..882S, doi:10.1086/176783.
- Ness, J.-U.; Jordan, C. (April 2008), "The corona and upper transition region of ε Eridani", Monthly Notices of the Royal Astronomical Society 385 (4): 1691–1708, arXiv:0711.3805, Bibcode:2008MNRAS.385.1691N, doi:10.1111/j.1365-2966.2007.12757.x.
- Wood, Brian E.; Müller, Hans-Reinhard; Zank, Gary P.; Linsky, Jeffrey L. (July 2002), "Measured mass-loss rates of solar-like stars as a function of age and activity", The Astrophysical Journal 574 (1): 1–2, arXiv:astro-ph/0203437, Bibcode:2002ApJ...574..412W, doi:10.1086/340797. See p. 10.
- Birney, D. Scott; González, Guillermo; Oesper, David (2006), Observational astronomy (2nd ed.), Cambridge, U.K.: Cambridge University Press, p. 75, ISBN 0-521-85370-2.
- de Mello, G. F. Porto; del Peloso, E. F.; Ghezzi, Luan (2005), "Astrobiologically interesting stars within 10 parsecs of the Sun", Astrobiology 6 (2): 308–331, arXiv:astro-ph/0511180, Bibcode:2006AsBio...6..308P, doi:10.1089/ast.2006.6.308, PMID 16689649.
- Fuhrmann, K. (January 2004), "Nearby stars of the Galactic disk and halo. III", Astronomische Nachrichten 325 (1): 3–80, Bibcode:2004AN....325....3F, doi:10.1002/asna.200310173.
- King, Jeremy R. et al. (April 2003), "Stellar kinematic groups. II. A reexamination of the membership, activity, and age of the Ursa Major group", The Astronomical Journal 125 (4): 1980–2017, Bibcode:2003AJ....125.1980K, doi:10.1086/368241.
- Deltorn, J.-M.; Greene, P. (May 16, 2001), Jayawardhana, Ray; Greene, Thoas, ed., "Search for nemesis encounters with Vega, epsilon Eridani, and Fomalhaut", Young Stars Near Earth: Progress and Prospects (San Francisco, CA: Astronomical Society of the Pacific) 244: 227–232, arXiv:astro-ph/0105284, Bibcode:2001ASPC..244.....J, ISBN 1-58381-082-X.
- García-Sánchez, J. et al. (November 2001), "Stellar encounters with the Solar System", Astronomy and Astrophysics 379 (2): 634–659, Bibcode:2001A&A...379..634G, doi:10.1051/0004-6361:20011330.
- Wright, Jason; Marcy, Geoff (July 2010), Catalog of nearby exoplanets, California Planet Survey consortium, retrieved 2010-11-07.
- Butler, R. P. et al. (2006), "Catalog of nearby exoplanets", The Astrophysical Journal 646: 505–522, arXiv:astro-ph/0607493, Bibcode:2006ApJ...646..505B, doi:10.1086/504701.
- Reidemeister, M. et al. (March 2011), "The cold origin of the warm dust around ε Eridani", Astronomy & Astrophysics 527: A57, arXiv:1011.4882, Bibcode:2011A&A...527A..57R, doi:10.1051/0004-6361/201015328.
- Davis, G. R. et al. (February 2005), "Structure in the ε Eridani debris disk", The Astrophysical Journal 619 (2): L187–L190, arXiv:astro-ph/0208279, Bibcode:2005ApJ...619L.187G, doi:10.1086/428348.
- Morbidelli, A.; Brown, M. E.; Levison, H. F. (June 2003), "The Kuiper Belt and its primordial sculpting", Earth, Moon, and Planets 92 (1): 1–27, Bibcode:2003EM&P...92....1M, doi:10.1023/B:MOON.0000031921.37380.80.
- Coulson, I. M.; Dent, W. R. F.; Greaves, J. S. (March 2004), "The absence of CO from the dust peak around ε Eri", Monthly Notices of the Royal Astronomical Society 348 (3): L39–L42, Bibcode:2004MNRAS.348L..39C, doi:10.1111/j.1365-2966.2004.07563.x.
- Ozernoy, Leonid M.; Gorkavyi, Nick N.; Mather, John C.; Taidakova, Tanya A. (July 2000), "Signatures of exosolar planets in dust debris disks", The Astrophysical Journal Letters 537 (2): L147–L151, arXiv:astro-ph/0007014, Bibcode:2000ApJ...537L.147O, doi:10.1086/312779.
- Kuchner, Marc J.; Stark, Christopher C. (October 2010), "Collisional grooming models of the Kuiper Belt dust cloud", The Astronomical Journal 140 (4): 1007–1019, arXiv:1008.0904, Bibcode:2010AJ....140.1007K, doi:10.1088/0004-6256/140/4/1007.
- Brogi, M.; Marzari, F.; Paolicchi, P. (May 2009), "Dynamical stability of the inner belt around Epsilon Eridani", Astronomy and Astrophysics 499 (2): L13–L16, Bibcode:2009A&A...499L..13B, doi:10.1051/0004-6361/200811609.
- Clavin, Whitney (October 27, 2008), "Closest planetary system hosts two asteroid belts", NASA/JPL-Caltech, retrieved 2010-07-04.
- Liu, Wilson M. et al. (March 2009), "Observations of Main-Sequence Stars and Limits on Exozodical Dust with Nulling Interferometry", The Astrophysical Journal 693 (2): 1500–1507, Bibcode:2009ApJ...693.1500L, doi:10.1088/0004-637X/693/2/1500.
- Setiawan, J. et al. (2008), "Planets Around Active Stars", in Santos, N.C.; Pasquini, L.; Correia, A.; Romaniello, M, Precision spectroscopy in astrophysics, ESO Astrophysics Symposia, Garching, Germany: European Southern Observatory, pp. 201–204, arXiv:0704.2145, Bibcode:2008psa..conf..201S, doi:10.1007/978-3-540-75485-5_43, ISBN 978-3-540-75484-8.
- Heinze, A. N. et al. (November 2008), "Deep L'- and M-band imaging for planets around Vega and ε Eridani", The Astrophysical Journal 688 (1): 583–596, arXiv:0807.3975, Bibcode:2008ApJ...688..583H, doi:10.1086/592100.
- Veras, Dimitri; Armitage, Philip J. (January 2004), "Outward migration of extrasolar planets to large orbital radii", Monthly Notices of the Royal Astronomical Society 347 (2): 613–624, arXiv:astro-ph/0310161, Bibcode:2004MNRAS.347..613V, doi:10.1111/j.1365-2966.2004.07239.x.
- McCarthy, Chris (2008), Space Interferometry Mission: key science project, Exoplanets Group, San Francisco State University, retrieved 2008-07-22.
- McNutt, R. L. et al. (January 19, 2000), "A realistic interstellar explorer", AIP Conference Proceedings, Space Technology and Applications International Forum 504, pp. 917–924, Bibcode:2000AIPC..504..917M, doi:10.1063/1.1302595.
- Kitzmann, D. et al. (February 2010), "Clouds in the atmospheres of extrasolar planets. I. Climatic effects of multi-layered clouds for Earth-like planets and implications for habitable zones", Astronomy and Astrophysics 511: 511A66.1–511A66.14, arXiv:1002.2927, Bibcode:2010A&A...511A..66K, doi:10.1051/0004-6361/200913491. See table 3.
- Underwood, David R.; Jones, Barrie W.; Sleep, P. Nick (2003), "The evolution of habitable zones during stellar lifetimes and its implications on the search for extraterrestrial life", International Journal of Astrobiology 2 (4): 289–299, arXiv:astro-ph/0312522, Bibcode:2003IJAsB...2..289U, doi:10.1017/S1473550404001715.
- Jones, Barrie W.; Underwood, David R.; Sleep, P. Nick (April 22–25, 2003), "The stability of the orbits of Earth-mass planets in and near the habitable zones of known exoplanetary systems", Proceedings of the Conference on Towards Other Earths: DARWIN/TPF and the Search for Extrasolar Terrestrial Planets, Heidelberg, Germany: Dordrecht, D. Reidel Publishing Co, pp. 625–630, arXiv:astro-ph/0305500, Bibcode:2003ESASP.539..625J, ISBN 92-9092-849-2.
- Marcy, G. et al. (February 12, 2002), A Planet Around Epsilon Eridani?, Exoplanets.org, retrieved 2011-05-18.
- Staff (July 8, 1998), "Astronomers discover a nearby star system just like our own Solar System", Joint Astronomy Centre (The University of Hawaii), retrieved 2011-02-24.
- Anonymous, "Epsilon Eridani", SolStation (The Sol Company), retrieved 2008-11-28.
- Tirion, Wil (2001), "Sky Map: Epsilon Eridani", Planet Quest (Cambridge, U.K.: Cambridge University Press), retrieved 2011-04-09.