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Epsilon Eridani

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Epsilon Eridani

Posisi ε Eridani
Data pengamatan
Epos J2000.0      Ekuinoks J2000.0
Rasi bintang Eridanus
Asensio rekta  03j 32m 55.8442d[1]
Deklinasi  −09° 27′ 29.744 ″[1]
Magnitudo tampak (V) 3.73[1]
Ciri-ciri
Kelas spektrum K2V[1]
Magnitudo semu (B) ~4.61[1]
Magnitudo semu (V) ~3.73[1]
Magnitudo semu (J) 2.228 ±0.298[1]
Magnitudo semu (H) 1.880 ±0.276[1]
Magnitudo semu (K) 1.776 ±0.286[1]
Indeks warna U−B +0.58[2]
Indeks warna B−V +0.88[2]
Indeks warna V−R +0.50
Indeks warna R−I +0.42
Jenis variabel BY[1][3]
Astrometri
Kecepatan radial (Rv)+15.5±0.9[1] km/s
Gerak diri (μ) RA: −976.36[1] mdb/thn
Dek.: 17.98[1] mdb/thn
Paralaks (π)310,74±0,85[1] mdb
Jarak10,50 ± 0,03 tc
(3,218 ± 0,009 pc)
Magnitudo mutlak (MV)6.19[4]
Detail
Massa0.85[4] M☉
Radius0.84[5] R☉
Luminositas0.28 L☉
Gravitasi permukaan (log g)4.57[6]
Suhu5073±42[7] K
Metalisitas[Fe/H]=−0.13±0.04[7]
Rotasi11.1 days
Usia(0.5–1.0) × 109[8] tahun
Referensi basis data
SIMBADdata
Extrasolar Planets
Encyclopaedia		data
Penamaan lain
18 Eridani, BD -09°697, GCTP 742.00, GJ 144, HD 22049, HIP 16537, HR 1084, LHS 1557, SAO 130564, WDS 03330-0928[1]

Epsilon Eridani (ε Eri / ε Eridani) adalah bintang deret-utama dengankelas spektrum K2. Berjarak sekitar 10.5 tahun cahaya dari matahari, merupakan rasi bintangEridanus, as well as the third closest star yang nampak dengan mata telanjang. Usianya diperkirakan setidaknya kurang dari satu milyar tahun. Because of its relative youth, Epsilon Eridani has a higher level of magnetic activity than the Sun, with a stellar wind 30 times as strong. Its rotation period is a relatively rapid 11.1 days, although this varies by latitude. Epsilon Eridani is both smaller and less massive than the Sun, with a lower metallicity (enrichment in elements heavier than helium).[8]

Radial velocity observations over the past 20 years yield evidence of a gas giant planet orbiting Epsilon Eridani, making it the nearest extrasolar system with a candidate exoplanet.[9] This object, conventionally known as Epsilon Eridani b, was formally announced in 2000 by a team of astronomers led by Artie Hatzes.[9] However, the radial velocity data contain a high level of background noise due to the star's magnetic activity, and the proposed planet is not universally accepted.[10] Current data indicate that this planet orbits in a period of about 7 years at a mean separation of 3.4 astronomical units (AU), corresponding to 505 million kilometers.[11]

The system also includes two debris belts composed of rocky asteroids, one at about 3 AU and the second at about 20 AU, whose structure may be maintained by a hypothetical second planet.[12] In addition, Epsilon Eridani harbors an extensive outer debris disk corresponding to the Solar System's Kuiper belt.[10] The density of orbiting material, which is considerably more than that around the Sun, corroborates the star's youth.

As one of the nearest Sun-like stars, Epsilon Eridani regularly appears in science fiction. Its closest neighbor is the M dwarf binary system Luyten 726-8, at a distance of about 5 light years.[13]

Observation

This star is located in the northern part of the constellation Eridanus, about 3° east of the slightly brighter star Delta Eridani. With a declination of −9.45°, 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.[14] The apparent magnitude of 3.73 can make this star difficult to observe from an urban area with the unaided eye, as the night skies over cities are illuminated by light pollution.[15]

The Bayer designation for this star was established in 1603 as part of the Uranometria, a star catalog produced by Johann Bayer. Epsilon is the fifth letter in the Greek alphabet, and it was assigned to the fifth brightest star in the constellation of Eridanus.[16] The preliminary version of the star catalog by John Flamsteed, published in 1712, gave this star the Flamsteed designation 18 Eridani.[1] In 1918 this star appeared in the Henry Draper Catalogue with the designation HD 22049 and a preliminary spectral classification of K0.[17]

Based on observations between 1800 and 1880, Epsilon Eridani was found to have a large proper motion, which at the time was estimated at three arcseconds annually. This implied a relatively close proximity to the Sun,[18] making it a star of interest for the purpose of trigonometric parallax measurements.[19] From 1881–3, William L. Elkin made a series of heliometric measurements from the Royal Observatory at the Cape of Good Hope, South Africa. As a result of these observations, a preliminary parallax of 0.14 ± 0.02 arcseconds was computed for Epsilon Eridani.[20][21] By 1917, observers had refined their parallax estimate to 0.317 arcseconds,[22] which is quite close to the modern value of 0.3107 arcseconds.[1] This parallax is equivalent to a distance of about 10.5 light years, making Epsilon Eridani the 13th nearest known star (and ninth nearest stellar system) to the Sun.[4]

In 1960, Project Ozma, headed by Dr. Frank Drake, used a radio telescope at Green Bank, West Virginia, to search for signals from putative extraterrestrial intelligences. Its target stars were Epsilon Eridani and Tau Ceti. However, no signals of extraterrestrial origin were detected.[23]

In 1983, NASA's orbiting telescope IRAS detected excess infrared emissions originating from Epsilon Eridani, indicating the presence of an orbiting disk of fine-grained dust.[24][25] This so-called debris disk has been extensively studied since that time.

In 1995, based on its location within 7.2 pc, Epsilon Eridani was among the target stars of Project Phoenix, a microwave survey for signals from extraterrestrial intelligence.[26] By 2004 Project Phoenix had checked about 800 stars, but had not yet detected an unimpeachable signal.[27]

Based on perturbations in the position of Epsilon Eridani between 1938 and 1972, it was suspected that the star had an unseen companion with an orbital period of 25 years.[28] However, this claim was refuted in 1993. Radial velocity observations between 1980 and 2000 then provided convincing evidence of a planet orbiting the star with a period of about seven years.[9] The evidence for a planetary system was further strengthened in 1998 by the discovery of asymmetries in the dust ring around star. These clumps of dust could be explained by interaction with a planet orbiting just inside the dust ring.[29]

Karakteristik

Ukuran relatif Epsilon Eridani (kiri) dibandingkan dengan Matahari (kanan).

Epsilon Eridani diperkirakan memiliki 85% dari masa matahari[4] dan radiusnya 84% dari radius matahari,[5] tetapi memiliki hanya 28% tingkat luminositas dibanding matahari. Bintang ini merupakan bintang K dengan kelas spektrum terdekat, setelah Alpha Centauri B.[4] kandungan metallisitas atau zat-zat yang lebih berat dari helium sedikit lebih rendah dari matahari , dengan tingkat kromosferik besi diperkirakan 74% dari matahari.[7]

The chromosphere of Epsilon Eridani is more magnetically active than the Sun's. Approximately 9% of the deep photosphere is found to have a magnetic field with a strength about 0.14 teslas.[30] The overall magnetic activity level of this star is irregular, but it may vary with a five-year period. Assuming that the radius of the star does not change over this interval, then the variation in activity level appears to produce a temperature variation of 15 K, which corresponds to a magnitude variation of 0.014.[31]

Rotational modulation of the magnetic activity suggests that the equator of the star rotates with a period of 11.10 ± 0.03 days, which is less than half of the rotation period of the Sun. Stars that vary in magnitude because of magnetic activity coupled with rotation are classified as BY Draconis variables.[3] Observations have show this star to vary as much as 0.050 in magnitude due to starspots and other short-term magnetic activity.[32] Photometry has also shown that the surface of Epsilon Eridani, like the Sun, is undergoing differential rotation. That is, the rotation period at the surface varies by latitude, with the measured periods ranging from 10.8 to 12.3 days.[31] The axial tilt of this star remains uncertain, with estimates ranging from a low of 24° up to 72°.[33]

The high level of chromospheric activity, strong magnetic field, and relatively fast rotation rate indicate that this is a young star.[34] Computer models give an estimated age of 700–850 million years, although the actual age may be a low as 500 million or as high as a billion years.[8] However, the somewhat low abundance of heavy elements is characteristic of a much older star. This anomaly might be caused by a diffusion process that has transported some of the helium and heavier elements out of the photosphere to a region below the star's outer convection zone.[35]

Relative to the Sun, the outer atmosphere of Epsilon Eridani appears both larger and hotter. This is caused by a 30-fold higher mass loss rate from the star's stellar wind. The wind is generating an astrosphere that spans about 8,000 AU and a bow shock that lies 1,600 AU from the star. At the star's estimated distance from the Earth, this astrosphere would span an angle of 42 arcminutes, which is wider than the appearance of a full Moon.[36]

The space velocity components of Epsilon Eridani are U = −3 km/s, V = +7 km/s and W = −20 km/s. It is orbiting within the Milky Way at a mean galactocentric distance of 8.8 kpc and an orbital eccentricity of 0.09.[37] During the past million years, three stars are believed to have come within two parsecs of Epsilon Eridani. The most recent encounter was with Kapteyn's Star, which approached within about a parsec about 12,500 years ago. None of these encounters are thought to have affected the circumstellar disk.[38] Epsilon Eridani made its closest approach to the Solar System about 105,000 years ago, when the two stars were separated by seven light years.[39]

Sistem planet

Templat:PlanetboxOrbit begin Templat:PlanetboxOrbit disk Templat:PlanetboxOrbit Templat:PlanetboxOrbit disk Templat:PlanetboxOrbit speculation

|- | Dust disk | colspan="4"| 35–100 AU | — | — Templat:PlanetboxOrbit end


Catatan kaki and referensi

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  2. ^ a b Mendoza, E. E. (1978). "UBVRI photometry of 225 Am stars". Astronomical Journal. 83: 606–614. doi:10.1086/112242. Diakses tanggal 2007-11-29. 
  3. ^ a b "GCVS Query=eps Eri". General Catalog of Variable Stars. Sternberg Astronomical Institute, Moscow, Russia. Diakses tanggal 2009-05-20. 
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Pranala luar

Koordinat: Peta langit 03h 32m 55.8442s, −09° 27′ 29.744″

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