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{{Starbox begin
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  | name=Epsilon Eridani
}}
{{Starbox image
| image =
    <div style="position: relative">[[File:Eridanus IAU.svg|250px|alt=Diagram showing star positions and boundaries of the Eridanus constellation and its surroundings]]
    <div style="position: absolute; left: 49.9%; top: 20.3%">[[File:Cercle rouge 100%.svg|12px]]</div>
    </div>
| caption = A [[star chart]] of the Eridanus constellation showing the position of ε Eridani (circled)
}}
{{Starbox observe
| epoch=[[J2000.0]]
| constell=[[Eridanus (constellation)|Eridanus]]
| ra={{RA|03|32|55.84496}}<ref name=aaa474_2_653/>
| dec={{DEC|−09|27|29.7312}}<ref name=aaa474_2_653/>
| appmag_v=3.736<ref name=saaoc8_59/>
}}
{{Starbox character
| class=K2V<ref name=aj132_1_161/>
| appmag_1_passband=B
| appmag_1 =~4.61<ref name=SIMBAD/>
| appmag_2_passband=V
| appmag_2=~3.73<ref name=SIMBAD/>
| appmag_3_passband=J
| appmag_3 ={{nowrap|2.228 ±0.298}}<ref name=cutri2003/>
| appmag_4_passband=H
| appmag_4 ={{nowrap|1.880 ± 0.276}}<ref name=cutri2003/>
| appmag_5_passband=K
| appmag_5 ={{nowrap|1.776 ± 0.286}}<ref name=cutri2003/>
| b-v=+0.887<ref name=saaoc8_59/>
| u-b=+0.571<ref name=saaoc8_59/>
| variable=[[BY Draconis variable|BY Dra]]<ref name=SIMBAD/><ref name=gcvs/>
}}
{{Starbox astrometry
| radial_v={{nowrap|+15.5 ± 0.9}}<ref name=rgcrv66/>
| prop_mo_ra=−975.17<ref name=aaa474_2_653/>
| prop_mo_dec=19.49<ref name=aaa474_2_653/>
| parallax=310.94
| p_error=0.16
| parallax_footnote=<ref name=aaa474_2_653/>
| absmag_v=6.19<ref name=RECONS/>
}}
{{Starbox detail
| age_gyr=0.2−0.8<ref name=aaa488_2_771/>
| metal_fe={{nowrap|−0.13 ± 0.04}}<ref name=aaa415/>
| mass={{nowrap|0.82 ± 0.02}}<ref name=mnras403_3_1368/><ref name=Baines/>
| radius={{nowrap|0.735 ± 0.005}}<ref name=aaa505_1_205/>
| rotation=11.2 days<ref name=an328_10/>
| rotational_velocity={{nowrap|2.4 ± 0.5}}<ref name=an328_10/>
| gravity={{nowrap|4.30 ± 0.08}}<ref name=mnras403_3_1368/>
| luminosity=0.34<ref name=apj460_993/>
| temperature={{nowrap|5,084 ± 5.9}}<ref name=aaa411_3_559/>
}}
{{Starbox reference
| Simbad = HD+22049
| NSTED =eps+Eridani
| EPE=eps+Eridani
}}
{{Starbox catalog
| names = [[Flamsteed designation|18&nbsp;Eridani]], [[Bonner Durchmusterung|BD]]&nbsp;-09°697, [[General Catalogue of Trigonometric Parallaxes|GCTP]]&nbsp;742.00, [[Gliese-Jahreiss catalogue|GJ]]&nbsp;144, [[Henry Draper catalogue|HD]]&nbsp;22049, [[Hipparcos catalogue|HIP]]&nbsp;16537, [[Harvard Revised catalogue|HR]]&nbsp;1084, [[Luyten Half-Second catalogue|LHS]]&nbsp;1557, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]]&nbsp;130564, [[Washington Double Star Catalog|WDS]]&nbsp;03330-0928.<ref name=SIMBAD/>
}}
{{Starbox end}}
'''Epsilon Eridani''' ('''ε Eri''', '''ε Eridani''') is a star in the southern constellation [[Eridanus (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 year]]s (ly), it has an [[apparent magnitude]] of 3.73. It is the [[List of nearest stars|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 [[Stellar magnetic field|magnetic activity]] than the present-day Sun, with a [[stellar wind]] 30 times as strong. Its rotation period is 11.2&nbsp;days at the equator. Epsilon Eridani is smaller and less massive than the Sun, and has a comparatively lower level of [[metallicity|elements heavier than helium]].<ref name="aaa426"/> It is a [[main sequence|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&nbsp;[[Kelvin|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 [[Methods of detecting extrasolar planets#Radial velocity|yielded evidence]] of a [[giant planet]] orbiting Epsilon Eridani, making it one of the nearest extrasolar system with a candidate [[exoplanet]].<ref name=apj544_2_L145/> This object, [[Epsilon Eridani b]], was formally announced in 2000 by a team of astronomers led by [[Artie P. Hatzes|Artie Hatzes]].<ref name=apj544_2_L145/> 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&nbsp;AU is the mean distance between the Earth and the Sun.<ref name=eep_eps_eri/> Although this discovery has been controversial because of the amount of background noise in the radial velocity data,<ref name=asp2003/> many astronomers now regard the planet as confirmed.
 
The system includes two belts of rocky [[asteroid]]s: one at about 3&nbsp;AU and a second at about 20&nbsp;AU, whose structure may be maintained by a hypothetical second planet, Epsilon Eridani c.<ref name=aguilar_pulliam20081027/> Epsilon Eridani harbors an extensive outer [[debris disk]] of remnant [[planetesimal]]s left over from the system's formation.<ref name=apj690_2_1522 />
 
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&nbsp;years when they will be separated by about 0.93&nbsp;ly.<ref name=potemine10/> As one of the nearest [[Solar analog|Sun-like stars]] with the potential for a planet that may harbor life,<ref name=villard35_12_44/> 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]].<ref name=boyle2009/>
 
== Observation history ==
{{Condense|section|date=October 2013}}
 
===Ptolemy===
[[File:Epsilon Eridani location.png|right|thumb|Above, the northern section of the Eridanus constellation is delineated in green, whilst the blue lines outline [[Orion (constellation)|Orion]]. Below, an enlarged view of the region in the white box shows the location of Epsilon Eridani at the intersection of the two lines.|alt=The upper photograph shows a region of many point-like stars with colored lines marking the constellations. The lower image shows several stars and two white lines.]]
Epsilon Eridani is known to astronomers at least from 2nd century, when it was catalogued by [[Claudius Ptolemy]], a [[Greek astronomy|Greek astronomer]] from [[Alexandria]], [[Egypt]], in his catalogue of more than 1000 stars. The catalogue was included as 7th (northern sky) and 8th (southern sky) books to his 13-book astronomical treatise ''[[Almagest|Μαθηματικὴ Σύνταξις (Mathēmatikē Syntaxis)]]'', known by its later Arabic name ''Almagest''. Constellation {{constel|Eri}}, named by Ptolemy ''"Ποταμού"'' (''"River"''), was included to 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 language|Greek]] ''"a foregoing of the four"''. The ''"four"'' is a group of four stars in Eridanus: [[Gamma Eridani|γ]], [[Pi Eridani|π]], [[Delta Eridani|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"''. [[apparent magnitude|Magnitude]], assigned to Epsilon Eridani by Ptolemy, was 3.{{r|Baily1843|Verbunt2012}}
 
===Al-Sufi, Al-Biruni and Ulugh Beg===
Then Epsilon Eridani was included to star catalogues of [[Astronomy in medieval Islam|medieval Islamic]] astronomical treatises, which were based on Ptolemy's catalogue: in [[Abd al-Rahman al-Sufi|Al-Sufi]]'s ''[[Book of Fixed Stars]]'', published in 964, [[Abū Rayḥān al-Bīrūnī|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 magnitude was 3. Al-Biruni quotes magnitudes from Ptolemy and Al-Sufi (however, for Epsilon Eridani he quotes value 4 for both Ptolemy and Al-Sufi magnitudes, whereas original values of both these magnitudes are 3). Its number in order of appearance is 786.{{r|Al-Biruni1030}} Ulugh Beg carried out new measurements of Epsilon Eridani's coordinates on his [[Ulugh Beg Observatory|observatory]], [[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).{{r|Baily1843|Verbunt2012}}
 
===Tycho Brahe===
In 1598 Epsilon Eridani was included to [[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 language|Latin]] ''"Which precedes all four"'', the meaning is the same as the Ptolemy's designation. Brahe assigned it magnitude 3.{{r|Baily1843|Verbunt2010a}}
 
===Bayer===
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,<ref name=jha17_50_189/> the star is the tenth [[List of stars in Eridanus|brightest star in Eridanus]].<ref name=ybsc1991/>
 
In addition to the letter ε, Bayer had given it a number 13 (the same as Ptolemy's catalogue number, as 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 [[Rigel|the foot]] of {{constel|Ori}} 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.{{r|Bayer1603}}
 
Bayer assigned Epsilon Eridani magnitude 3.{{r|Bayer1603}}
 
===Hevelius===
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 was assigned magnitude 3 (according Verbunt & Gent) or 4 (according Baily).{{r|Baily1843|Verbunt2010b}}
 
===Flamsteed===
The star catalogue of English astronomer [[John Flamsteed]], published in 1712, gave Epsilon Eridani the [[Flamsteed designation]] 18&nbsp;Eridani because it was the eighteenth catalogued star in the constellation of Eridanus by order of increasing right ascension.<ref name=SIMBAD/>
 
===Bradley===
Epsilon Eridani was included to [[James Bradley]]'s catalogue (because it has an entry in "Diff. of Bradley's Catalogue" column in ''Baily (1831)'').{{r|Baily1831}}
 
===Lacaille===
Then Epsilon Eridani appears in [[Nicolas Louis de Lacaille]] Catalogue of 398 principal Stars, whose 307-star version was published in 1755 in the ''Ephémérides des Mouvemens Célestes, pour dix années, 1755—1765'',{{r|Lacaille1755}} and whose full version was published in 1757 in ''Astronomiæ Fundamenta, Paris''.{{r|Lacaille1757}} In its 1831 edition by [[Francis Baily]] Epsilon Eridani has the number 50.{{r|Baily1831}} Lacaiile assigned it magnitude 3.{{r|Lacaille1755|Lacaille1757|Baily1831}}
 
===Lalande===
In 1801 Epsilon Eridani was included to ''[[Histoire Céleste Française]]'', a catalogue of about 50000 stars of [[Joseph Jérôme Lefrançois de Lalande]], 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).{{r|Lalande1801}}
 
In 1847 was published an edition of the Lalande's catalogue ([[Francis Baily]] ''et al.''), 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.{{r|Baily1847}} (Today numbers from this catalogue are used with prefix "Lalande", or "Lal").{{r|Lal}}
 
Lalande assigned Epsilon Eridani magnitude 3.{{r|Lalande1801|Baily1847}}
 
===Bode===
Also in 1801 it was included to catalogue of [[Johann Bode]], in which about 17000 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 southern sky), and an observer for Epsilon Eridani was Lalande. Bode assigned Epsilon Eridani magnitude 3.{{r|Bode1801}}
 
===Piazzi===
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.{{r|Piazzi1814}}
 
===Henry Draper Catalogue===
In 1918 Epsilon Eridani appeared in the [[Henry Draper Catalogue]] with the designation HD&nbsp;22049 and a preliminary spectral classification of K0.<ref name=ahco91_1/>
 
===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 [[arcsecond]]s annually.<ref name=mras48_77/> This movement implied it was relatively close to the Sun,<ref name=belkora2002/> making it a star of interest for the purpose of trigonometric [[parallax]] measurements. This process involves recording the position of Epsilon Eridani as Earth moves around the Sun, which allows a star's distance to be estimated.<ref name=mras48_77/> From 1881 to 1883, American astronomer [[William Lewis Elkin|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 {{nowrap|0.14 ± 0.02 arcseconds}} was calculated.<ref name=gill1893/><ref name=gill1884/> By 1917, observers had refined their parallax estimate to 0.317&nbsp;arcseconds.<ref name=apj46_313/> The modern value of 0.3109&nbsp;arcseconds is equivalent to a distance of about {{convert|10.50|ly|pc|abbr=in}}.<ref name=aaa474_2_653/>
 
===Circumstellar discoveries===
 
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&nbsp;years was causing gravitational [[Perturbation (astronomy)|perturbation]]s in its position.<ref name=aj79_491/> 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.<ref name=aj105_3_1188/>
 
Launched in 1983, the [[space telescope]] [[IRAS]] detected [[Infrared astronomy|infrared]] emissions from stars near to the Sun.<ref name=apj278_L1/> Two years later, the presence of an [[infrared excess|excess infrared emission]] close to Epsilon Eridani was announced, which indicated a disk of fine-grained [[cosmic dust]] was orbiting Epsilon Eridani.<ref name=pasp97_885/> 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.<ref name=apj506_2_L133/>
 
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.<ref name=apj544_2_L145/> Although there is a high level of noise in the radial velocity data due to magnetic activity in its [[photosphere]],<ref name=iau202/> any periodicity caused by this magnetic activity is expected to show a strong correlation with variations in [[emission line]]s of ionized calcium (the [[Calcium#H and K lines|Ca II H and K lines]]). Because no such correlation was found, a planetary companion was deemed the most likely cause.<ref name=apj133_6_2442/> 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.<ref name=aj132_2206/>
 
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.<ref name=apj578_2_L149/>
 
===SETI and proposed exploration===
 
In 1960, American physicist [[Philip Morrison]] and Italian physicist [[Giuseppe Cocconi]] proposed that [[extraterrestrial civilization]]s might be using radio signals for communication.<ref name=gugliucci20100524/> [[Project Ozma]], headed by American astronomer [[Frank Drake]], used the [[Tatel Telescope]] to search for such signals from the nearby [[Solar-type star|Sun-like stars]] Epsilon Eridani and [[Tau Ceti]]. They were observed at the emission frequency of [[neutral hydrogen]], 1,420&nbsp;MHz. No signals of intelligent extraterrestrial origin were detected.<ref name=heidmann_dunlop1995/> The experiment was repeated by Drake in 2010, with the same negative result.<ref name=gugliucci20100524/> Despite this lack of success, Epsilon Eridani made its way into [[Epsilon Eridani in fiction|science fiction literature and television shows]] for many years following news of Drake's initial experiment.<ref name=marschall_maran2009/>
 
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&nbsp;ly, it was listed with the 14 stars that were thought most likely to have a habitable planet.<ref name=dole1964/>
 
A new strategy in the search for extraterrestrial intelligence ([[SETI]]) was proposed by American space scientist [[William I. McLaughlin]] 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.<ref name=baas20_1043/>
 
Because of the proximity and Sun-like properties of Epsilon Eridani, it was considered as one of the targets for [[interstellar travel]] by American physicist [[Robert L. Forward]] in 1985.<ref name=jsr22_345/> The following year, Epsilon Eridani was suggested as one of several targets in the [[Project Daedalus]] paper study by the [[British Interplanetary Society]].<ref name=jbis29_94/> It has continued to be among the targets of such proposals, as with [[Project Icarus (Interstellar Probe Design Study)|Project Icarus]] in 2011.<ref name=aa20110125/>
 
Based on its location within {{Convert|23.5|ly|pc|abbr=in}}, Epsilon Eridani was among the target stars of [[Project Phoenix (SETI)|Project Phoenix]], a 1995 [[microwave]] survey for signals from extraterrestrial intelligence.<ref name=henry_asp19930916/> The project had checked about 800 stars by 2004, but had not yet detected an unimpeachable signal.<ref name=whitehouse_bbc20040325/>
 
== Properties ==
[[File:Size epsilon eridani.png|left|thumb|Illustration of the relative sizes of Epsilon Eridani (left) and the Sun (right)|alt=A glowing orange orb on the left half and a slightly larger glowing yellow orb on the right against a black background]]
 
At a distance of {{convert|10.50|ly|pc|abbr=in}}, Epsilon Eridani is the 13th-nearest known star (and ninth nearest solitary star or [[stellar system]]) to the Sun as of 2014.<ref name=RECONS/> Its proximity makes it one of the most studied stars of its [[stellar classification]].<ref name=mnras398_3_1495/> 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 &minus;9.46°, Epsilon Eridani can be viewed from much of the Earth's surface. Only to the north of [[80th parallel north|latitude 80&deg;&nbsp;N]] is it permanently hidden below the horizon.<ref name=campbell1899/> 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]].<ref name=narisada2004/>
 
Epsilon Eridani has an estimated 82% of the [[solar mass|Sun's mass]]<ref name=mnras403_3_1368/><ref name=Baines/> and 74% of the [[solar radius|Sun's radius]],<ref name=aaa505_1_205/> but only 34% of its [[solar luminosity|luminosity]].<ref name=apj460_993/> The estimated surface temperature is 5,084&nbsp;K.<ref name=aaa411_3_559/> With a stellar classification of K2&nbsp;V, it is the second-nearest [[K-type main-sequence star]] after [[Alpha Centauri|Alpha Centauri B]].<ref name=RECONS/> Indeed, since 1943, the [[spectrum]] of Epsilon Eridani has served as one of the stable anchor points by which other stars are classified.<ref name=baas25_1319/> 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.<ref name=aaa415/>
 
Epsilon Eridani's K-type classification indicates that the spectrum has relatively weak [[absorption line]]s from energy absorbed by hydrogen and strong lines of neutral atoms and singly [[ion]]ized [[Calcium#H and K lines|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 [[radiative transfer|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 [[Convection zone|plasma convection]], where it then radiates into space.<ref name=karttunen_oja2007/>
 
===Magnetic activity===
[[Image:Mass eject.png|right|thumb|An example of a region of magnetic activity on the surface of a star; in this case the Sun|alt=At left is a section of a red disk with an irregular bright region. Streams of red plasma trail off to the right.]]
 
Epsilon Eridani has a higher level of [[Stellar magnetic field|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 {{nowrap|(1.65 ± 0.30) × 10<sup>−2</sup> [[Tesla (unit)|T]]}},<ref name=aaa318_429/> which is more than forty times greater than the {{nowrap|(5–40) × 10<sup>−5</sup> T}} magnetic field strength in the Sun's photosphere.<ref name=apj591_2_1248/> The magnetic properties can be modeled by assuming that regions with a [[magnetic flux]] of about 0.14&nbsp;T randomly cover approximately 9% of the photosphere, whereas the remainder of the surface is free of magnetic fields.<ref name=apj1_439_2_939/> The overall magnetic activity of Epsilon Eridani is irregular, but it may vary with a 4.9-year period.<ref name=aaa483_3/> 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&nbsp;K, which corresponds to a variation in [[UBV photometric system|visual magnitude]] (V) of 0.014.<ref name=apj441/>
 
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 {{nowrap|15 m s}}<sup>&minus;1</sup> were measured over a 20&nbsp;year period, which is much higher than the measurement error rate of {{nowrap|3 m s}}<sup>&minus;1</sup>. This makes interpretation of periodicities in the radial velocity of Epsilon Eridani, such as those caused by the [[gravitational perturbation]]s of an orbiting planet, more difficult.<ref name=iau202/>
 
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.<ref name=gcvs/> Measurement of this rotational modulation suggests that its equatorial region rotates with an average period of 11.2&nbsp;days,<ref name=an328_10/> 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 [[starspot]]s and other short-term magnetic activity.<ref name=apj102_5_1813/> [[Photometry (astronomy)|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.<ref name=apj441/><ref name=rotation group=note/> The [[axial tilt]] of Epsilon Eridani toward the line of sight from Earth is uncertain. Estimates range from 24° to 72°.<ref name=an328_10/>
 
The high levels of chromospheric activity, strong magnetic field, and relatively fast rotation rate of Epsilon Eridani are characteristic of a young star.<ref name=apj1_412_2_797/> The age of Epsilon Eridani is about {{nowrap|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.<ref name=aaa488_2_771/> However, the low abundance of heavy elements in the chromosphere of Epsilon Eridani is indicative of an older star, because the [[interstellar medium|medium]] out of which stars form is steadily enriched by heavier elements produced by older generations of stars.<ref name=aaa358_850/> 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]].<ref name=cjaa8_5_591/>
 
The [[X-ray]] luminosity of Epsilon Eridani is about {{nowrap|2 × 10<sup>28</sup> [[erg]]s/s}} ({{nowrap|2 × 10<sup>21</sup> [[Watt|W]]}}). It is brighter in X-ray emission than the Sun at [[Solar cycle|peak activity]]. The source for this strong X-ray emission is Epsilon Eridani's hot corona.<ref name=apj243_234/><ref name=apj457_882/> Epsilon Eridani's corona appears larger and hotter than the Sun's, with a temperature of {{nowrap|3.4 × 10<sup>6</sup> K}} as measured from observation of the corona's ultraviolet and X-ray emission.<ref name=mnras385_4_1691/>
 
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.<ref name=mnras385_4_1691/> 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 [[Stellar wind bubble|astrosphere]] (the equivalent of the [[heliosphere]] that surrounds the Sun) that spans about 8,000&nbsp;AU and contains a [[bow shock]] that lies 1,600&nbsp;AU from Epsilon Eridani. At its estimated distance from Earth, this astrosphere spans 42&nbsp;arcminutes, which is wider than the apparent size of the full Moon.<ref name=apj574_1/>
 
===Kinematics===
Epsilon Eridani has a high [[proper motion]], moving −0.976&nbsp;arcseconds per year in right ascension (the celestial longitude) and 0.018&nbsp;arcseconds per year in declination (the celestial latitude), for a total proper motion of 0.962 arcseconds per year.<ref name=aaa474_2_653/>{{#tag:ref|The total proper motion μ can be computed from:
: μ<sup>2</sup> = (μ<sub>α</sub> cos δ)<sup>2</sup> + μ<sub>δ</sub><sup>2</sup>
where μ<sub>α</sub> is the proper motion in right ascension, μ<sub>δ</sub> is the proper motion in declination, and δ is the declination.<ref name="birney"/> This yields:
: μ<sup>2</sup> = (−975.17 · cos(−9.458°))<sup>2</sup> + 19.49<sup>2</sup> = 925658.1
or μ equals 962.11.|group="note"|name=total_pm}} It has a radial velocity of +15.5&nbsp;km/s away from the Sun.<ref name=rgcrv66/> The [[space velocity (astronomy)|space velocity]] components of Epsilon Eridani in the [[galactic coordinate system]] are {{nowrap|(U, V, W)}} = {{nowrap|(−3, +7, −20) km/s}}, which means that it is traveling within the [[Milky Way]] at a mean [[galactocentric distance]] of 28.7&nbsp;kly (8.79&nbsp;kiloparsecs) from the core along an orbit that has an [[orbital eccentricity|eccentricity]] of 0.09.<ref name=ab6_2_308/> The [[Stellar kinematics|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.<ref name=aaa488_2_771/><ref name=an325_1_3/> The estimated age of this group is {{nowrap|500±100 million}} years,<ref name=apj125_4_1980/> 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&nbsp;ly (2&nbsp;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&nbsp;ly (0.9&nbsp;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.<ref name=asp2001_227/>
 
Epsilon Eridani made its closest approach to the Sun about 105,000&nbsp;years ago, when they were separated by {{convert|7|ly|pc|abbr=in}}.<ref name=aaa379/> 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&nbsp;ly (0.29&nbsp;parsecs). They will be less than 1&nbsp;ly (0.3&nbsp;parsecs) apart for about 4,600 years. If Epsilon Eridani has an [[Oort cloud]], Luyten 726-8 could gravitationally [[Perturbation (astronomy)|perturb]] some of the [[Exocomet|comet]]s with long [[orbital period]]s.<ref name=potemine10/>
 
== Planetary system ==
{{OrbitboxPlanet begin
| table_ref=<ref name=apj690_2_1522/><ref name=aj132_2206/><ref name=cne2008/><ref name=apj646_505/>
| name=Epsilon Eridani
}}
{{OrbitboxPlanet disk
| disk = Asteroid belt
| periapsis = 3
}}
{{OrbitboxPlanet hypothetical
| exoplanet = [[Epsilon Eridani b|b]]
| mass = {{nowrap|1.55 ± 0.24}}
| period = {{nowrap|2,502–2,630}}
| semimajor = {{nowrap|3.38–3.50}}
| eccentricity = {{nowrap|0.25–0.702}}
}}
{{OrbitboxPlanet disk
| disk = Asteroid belt
| periapsis = 20
}}
{{OrbitboxPlanet hypothetical
| exoplanet = [[Epsilon Eridani c|c]]
| mass = 0.1
| period = 102,270
| semimajor = 40?
| eccentricity = 0.3
}}
{{OrbitboxPlanet disk
| disk = Dust disk
| periapsis = 35
| apoapsis = 100
}}
{{Orbitbox end}}
{{multiple image
| align    = right
| direction = vertical
| width    = 300
| image1    = Epsilon eridani dustring.gif
| width1    =
| alt1      = An uneven, multi-colored ring arranged around a five-sided star at the middle, with the strongest concentration below center. A smaller oval showing the scale of Pluto's orbit is in the lower right
| caption1  = Submillimeter wavelength image of a ring of dust particles around Epsilon Eridani (above center). The brightest areas indicate the regions with the highest concentrations of dust.
| image2    = System Epsilon Eridani.JPG
| width2    =
| alt2      = The upper two illustrations show brown oval bands for the asteroid belts and oval lines for the known planet orbits, with the glowing star at the center. The second brown band is narrower than the first. The lower two illustrations have gray bands for the comet belts, oval lines for the planetary orbits and the glowing stars at the center. The lower gray band is much wider than the upper gray band.
| caption2  = Comparison of the planets and debris belts in the Solar System to the Epsilon Eridani system. At the top is the asteroid belt and the inner planets of the Solar System. Second from top is the proposed inner asteroid belt and planet b of Epsilon Eridani. The lower illustrations show the corresponding features for the two stars' outer systems.
}}
 
=== Dust disk ===
Observations with the [[James Clerk Maxwell Telescope]] at a [[wavelength]] of 850&nbsp;μm show an extended flux of radiation out to an [[Angular diameter|angular radius]] of 35&nbsp;arcseconds around Epsilon Eridani. The peak emission occurs at an angular radius of 18&nbsp;arcseconds, which corresponds to a radius of about 60&nbsp;AU. The highest level of emission occurs over the radius 35–75 AU from Epsilon Eridani and is substantially reduced inside 30&nbsp;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.<ref name=apj506_2_L133/>
 
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]].<ref name=arxiv1011_4882/> 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.<ref name=apj690_2_1522/>
 
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&nbsp;μm in size at a temperature of about 55&nbsp;K. This dust is being generated by the collision of comets, which range up to 10 to 30&nbsp;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.<ref name=apj619_2_L187/><ref name=emp92_1_1/> However, the disk around Epsilon Eridani contains less than {{nowrap|2.2 &times; 10<sup>17</sup> kg}} of [[carbon monoxide]]. This low level suggests a paucity of volatile-bearing comets and icy [[planetesimal]]s compared to the Kuiper belt.<ref name=mnras348_3_L39/>
 
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]].<ref name=apjl_537_L147/> 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.<ref name=apj578_2_L149/> Alternatively, the clumpiness may have been caused by collisions between [[minor planet]]s known as [[plutino]]s.<ref name=aj140_4_1007/>
 
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 {{nowrap|3.00 &plusmn; 0.75 AU}} from Epsilon Eridani, and consists of [[silicate]] grains with a diameter of 3&nbsp;[[Micrometre|μm]] and a combined mass of about 10<sup>18</sup>&nbsp;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 [[asteroid]]s.<ref name=aaa499_2_L13/> 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.<ref name=apj690_2_1522/><ref name=spitzer20081027/>
 
In an alternative scenario, the exozodiacal dust may be generated in an outer belt, which is orbiting between 55 and 90&nbsp;AU from Epsilon Eridani and has an assumed mass of 10<sup>−3</sup> 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 (phase transition)|sublimation]], located beyond 10&nbsp;AU from Epsilon Eridani where the temperatures fall below 100&nbsp;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]].<ref name=arxiv1011_4882/>
 
The inner region around Epsilon Eridani, from a radius of 2.5&nbsp;AU inward, appears to be clear of dust down to the detection limit of the 6.5&nbsp;m [[MMT Observatory|MMT telescope]]. Grains of dust in this region are efficiently removed by drag from the stellar wind, whrtrsd 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.<ref name=apj693_2_1500/>
 
=== Possible planets ===
[[File:NASA-JPL-Caltech - Double the Rubble (PIA11375) (pd).jpg|right|thumb|An artist's illustration showing two asteroid belts and a planet orbiting Epsilon Eridani|alt=A bright light source at right is encircled by comets and two oval belts of debris. At left is a yellow-orange crescent of a planet.]]
As one of the nearest Sun-like stars, Epsilon Eridani has been the target of many attempts to search for planetary companions.<ref name=aaa488_2_771/><ref name=apj544_2_L145/> However, its chromospheric activity and variability means that finding planets with the [[Methods of detecting extrasolar planets#Radial velocity|radial velocity method]] is difficult, because the stellar activity may create signals that mimic the presence of planets.<ref name=setiawan2008/> Attempts at direct imaging of potential exoplanets have proven unsuccessful to date.<ref name=apj133_6_2442/><ref name=apj688_1_583/> Infrared observation has shown there are no bodies of three or more [[Jupiter mass]]es in this system.<ref name=aaa488_2_771/>
 
====Planet b====
{{further|Epsilon Eridani b}}
[[Extrasolar planet#Nomenclature|Referred to]] as [[Epsilon Eridani b|Epsilon Eridani&nbsp;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".<ref name=apj690_2_1522 /> However, many astronomers believe the evidence is sufficiently compelling that they regard the discovery as confirmed.<ref name=aaa488_2_771/><ref name=arxiv1011_4882/><ref name=aaa499_2_L13/><ref name=apj688_1_583/>
 
[[File:Epsilon Eridani b.jpg|thumb|left|Artist's impression of the proposed planet Epsilon Eridani&nbsp;b orbiting within a zone that has been cleared of dust. Near the bottom center is a conjectured moon.|alt=At left is a shadowed, spherical red object encircled by a ring, with a smaller crescent at lower center portraying a moon. To the right is a luminous source bisected by a line representing a debris disk.]]
 
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.<ref name=aj132_2206/> Estimates of the maximum radius of its elliptical orbit—the [[semimajor axis]]—range from 3.38 AU to 3.50 AU<ref name=cne2008/><ref name=apj646_505/> and approximations of its [[orbital eccentricity]] range from {{nowrap|0.25 ± 0.23}} to {{nowrap|0.702 ± 0.039}}.<ref name=aj132_2206/><ref name=apj646_505/>
 
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 [[Stellar rotation#Measurement|''m''&nbsp;sin&nbsp;''i'']], where ''m'' is the mass of the planet and ''i'' is the [[orbital inclination]]. Estimates for the value of {{nowrap|''m'' sin ''i''}} range from 0.60 [[Jupiter mass]]es to 1.06 Jupiter masses,<ref name=cne2008/><ref name=apj646_505/> 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 {{nowrap|1.55 ± 0.24}} Jupiter masses for the planet's mass.<ref name=aj132_2206/>
 
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&nbsp;b's eccentricity is inconsistent with the presence of the proposed asteroid belt at a distance of 3&nbsp;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&nbsp;b's eccentricity of about 0.10–0.15.<ref name=aaa499_2_L13/><ref name=spitzer20081027/> 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.<ref name=arxiv1011_4882/>
 
====Planet c====
[[Image:View epsilon eridani c.png|right|thumb|Rendered illustration of the unconfirmed second planet as seen from a hypothetical moon. The distant Epsilon Eridani is visible on the left, surrounded by a faint disk of dust particles.|alt=At left is a luminous point encircled by a nebulous gray belt. To the right is a crescent-shaped blue planet. Along the bottom is the rugged terrain of a moon surface.]]
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&nbsp;c. Clumping in the dust disk may occur because dust particles are being trapped in orbits that have [[Orbital resonance|resonant]] orbital periods with a planet in an eccentric orbit. The postulated Epsilon Eridani&nbsp;c would orbit at a distance of 40&nbsp;AU, with an eccentricity of 0.3 and a period of 280 years.<ref name=apj578_2_L149/> The inner cavity of the disk may be explained by the presence of additional planets.<ref name=aaa488_2_771/> 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&nbsp;AU then migrated outward because of gravitational interaction with the disc or with other planets in the system.<ref name=mnras347_2_613/>
 
====Potential habitability====
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.<ref name=mccarcty2008/> 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.<ref name=jsr22_345/><ref name=jbis29_94/><ref name=mcnutt2000/>
 
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).<ref name=aaa511/> 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&nbsp;AU. As Epsilon Eridani ages over a period of 20&nbsp;billion years, the net luminosity will increase, causing this zone to slowly expand outward to about 0.6–1.4&nbsp;AU.<ref name=ijab2_289/> 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.<ref name=jones_underwood_sleep2003/>
 
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&nbsp;AU.<ref name=asp2003/> Epsilon Eridani's proximity, Sun-like properties and suspected planets have made it a destination for [[interstellar travel]] in [[science fiction]] stories.<ref name=boyle2009/>
 
== See also ==
* [[Epsilon Eridani in fiction]]
* [[List of exoplanetary host stars]]
* [[List of extrasolar planets]]
* [[List of nearest stars]]
 
== Notes and references ==
 
===Notes===
{{Reflist|colwidth=50em|group=note|refs=
{{#tag:ref|The rotation period ''P<sub>β</sub>'' at latitude ''β'' is given by:
:''P<sub>β</sub>'' = ''P<sub>eq</sub>''/(1 &minus; ''k'' sin ''β'')
where ''P<sub>eq</sub>'' is the equatorial rotation period and  ''k'' is the differential rotation parameter. The value
of this parameter is estimated to be in the range:
:0.03 ≤ ''k'' ≤ 0.10<ref name=an328_10/>|group="note"|name=rotation}}
 
}}
 
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<ref name=Baines>{{citation | last1=Baines| first1=Ellyn K. | last2=Armstrong | first2=J. Thomas | title=Confirming Fundamental Parameters of the Exoplanet Host Star epsilon Eridani Using the Navy Optical Interferometer| journal=The Astrophysical Journal| year=2011| arxiv=1112.0447 }}</ref>
 
<ref name=Baily1843>{{rr/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)''.</ref>
 
<ref name=Verbunt2012>{{cite doi/10.1051.2F0004-6361.2F201219596|P=784|U=781}}</ref>
 
<ref name=Verbunt2010a>{{cite doi/10.1051.2F0004-6361.2F201014002|K=910}}</ref>
 
<ref name=Verbunt2010b>{{cite doi/10.1051.2F0004-6361.2F201014003|H=712}}</ref>
 
<ref name=Bayer1603>{{rr/Bayer1603|Eri}}</ref>
 
<ref name=Al-Biruni1030>{{rr/Al-Biruni1030}} ''(Epsilon Eridani: see page 135)''.</ref>
 
<ref name=Lacaille1755>{{rr/gbooks=CGHtdxdcc5UC}} ''(Epsilon Eridani: see page LV of the "Introduction")''.</ref>
 
<ref name=Lacaille1757>{{rr/gbooks=-VQ AAAAcAAJ}} ''(Epsilon Eridani: see page 233 (in the catalogue), see also pages 96, 153—154, 189, 231)''.</ref>
 
<ref name=Baily1831>{{rr/1831MNRAS...2...33B}} ''(Epsilon Eridani: see page 110)''.</ref>
 
<ref name=Lalande1801>{{rr/gbooks=f9AMAAAAYAAJ}} ''(Epsilon Eridani: see pages 246, 248, 307)''.</ref>
 
<ref name=Baily1847>{{rr/1847cshc.book.....B}} ''(Epsilon Eridani: see page 165)''.</ref>
 
<ref name=Lal>{{rr/Dic-Simbad|Lal}}</ref>
 
<ref name=Bode1801>{{rr/1801abun.book.....B}} ''(Epsilon Eridani: see page 71)''.</ref>
 
<ref name=Piazzi1814>{{rr/1814psip.book.....P}} ''(Epsilon Eridani: see page 22)''.</ref>
}}
 
== External links ==
*{{citation | display-authors=1 | last1=Marcy | first1=G. | last2=Butler | first2=P. | last3=Vogt | first3=S. | last4=Fischer | first4=D. | title=A Planet Around Epsilon Eridani? | date=February 12, 2002 | publisher=Exoplanets.org | url=http://exoplanets.org/esp/epseri/epseri.shtml | accessdate=2011-05-18 | postscript=. }}
*{{citation | author=Staff | title=Astronomers discover a nearby star system just like our own Solar System | date=July 8, 1998 | work=Joint Astronomy Centre | publisher=The University of Hawaii | url=http://outreach.jach.hawaii.edu/pressroom/1998_epseri/ | accessdate=2011-02-24 | postscript=. }}
*{{citation | author=Anonymous | title=Epsilon Eridani | work=SolStation | publisher=The Sol Company | url=http://www.solstation.com/stars/eps-erid.htm | accessdate=2008-11-28 | postscript=. }}
*{{citation | first1=Wil | last1=Tirion | title=Sky Map: Epsilon Eridani | publisher=Cambridge University Press | publication-place=Cambridge, U.K. | year=2001 | work=Planet Quest | url=http://planetquest1.jpl.nasa.gov/atlas/atlas_skymap.cfm?Planet=109&Zoom=1 | accessdate=2011-04-09 | postscript=. }}
 
{{Sky|03|32|55.8442|−|09|27|29.744|10.5}}
{{Nearest systems|3}}
{{Stars of Eridanus}}
 
{{featured article}}
 
[[Category:Bayer objects|Eridani, Epsilon]]
[[Category:Circumstellar disks]]
[[Category:Eridanus (constellation)]]
[[Category:Gliese and GJ objects|0144]]
[[Category:Henry Draper Catalogue objects|022049]]
[[Category:Hipparcos objects|016537]]
[[Category:HR objects|1084]]
[[Category:K-type main-sequence stars]]
[[Category:Solar-type stars|Eridani, Epsilon]]
[[Category:Planetary systems]]
[[Category:Stars with proper names]]
[[Category:Objects within 100 ly of Earth]]
 
{{Link GA|it}}

Latest revision as of 23:36, 15 October 2014

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