Astronomy:Epsilon Tauri
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| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Taurus |
| Right ascension | 04h 28m 37.0003s[1] |
| Declination | +19° 10′ 49.563″[1] |
| Apparent magnitude (V) | +3.53[2] |
| Characteristics | |
| Spectral type | K0III[2] |
| B−V color index | 1.014[3] |
| Astrometry | |
| Radial velocity (Rv) | 38.420±0.0004[4] km/s |
| Proper motion (μ) | RA: 107.526±0.193[1] mas/yr Dec.: −36.200±0.126[1] mas/yr |
| Parallax (π) | 22.3654 ± 0.1721[1] mas |
| Distance | 146 ± 1 ly (44.7 ± 0.3 pc) |
| Absolute magnitude (MV) | 0.145[5] |
| Details | |
| Mass | 2.57+0.17 −0.25[6] M☉ |
| Radius | 12.35+0.41 −0.36[6] R☉ |
| Luminosity | 78.11+5.68 −5.82[6] L☉ |
| Surface gravity (log g) | 2.66+0.03 −0.05[6] cgs |
| Temperature | 4,950±22[7] K |
| Metallicity [Fe/H] | +0.15±0.02[7] dex |
| Rotation | 141.1 days[6] |
| Rotational velocity (v sin i) | 3.0[5] km/s |
| Age | 625[2] Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Epsilon Tauri or ε Tauri, formally named Ain (/ˈeɪn/),[8] is an orange giant star located approximately 146 light-years (45 parsecs) from the Sun in the constellation of Taurus. An exoplanet (designated Epsilon Tauri b, later named Amateru) is believed to be orbiting the star.
It is a member of the Hyades open cluster. As such its age is well constrained at 625 million years.[2] It is claimed to be the heaviest among planet-harboring stars with reliable initial masses.[2] Given its large mass, this star, though presently of spectral type K0 III, was formerly of spectral type A that has now evolved off the main sequence into the giant phase. It is regarded as a red clump giant; that is, a core-helium burning star.[2]
Since Epsilon Tauri lies near the plane of the ecliptic, it is sometimes occulted by the Moon and (very rarely) by planets.
It has an 11th magnitude companion 182 arcseconds from the primary, although this is an unrelated background star.[9]
Nomenclature
ε Tauri (Latinised to Epsilon Tauri) is the star's Bayer designation; it also bears the Flamsteed designation of 74 Tauri. On discovery, the planet was designated Epsilon Tauri b (or Ain b).
The star bore the traditional name Ain (Arabic عين for "eye") and was given the name Oculus Boreus (Latin for "Northern eye") by John Flamsteed.[10][11] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[12] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[13] included a table of the first two batches of names approved by the WGSN; which included Ain for this star.
In July 2014, the International Astronomical Union launched NameExoWorlds, a process for giving proper names to certain exoplanets.[14] The process involved public nomination and voting for the new names.[15] In December 2015, the IAU announced the winning name was Amateru for this planet.[16]
The winning name was based on that submitted by the Kamagari Astronomical Observatory of Kure, Hiroshima Prefecture, Japan : namely 'Amaterasu', the Shinto goddess of the Sun, born from the left eye of the god Izanagi. The IAU substituted 'Amateru' – which is a common Japanese appellation for shrines when they enshrine Amaterasu – because 'Amaterasu' is already used for an asteroid (10385 Amaterasu).[17]
In Chinese, 畢宿 (Bì Xiù), meaning Net, refers to an asterism consisting ε Tauri, δ3 Tauri, δ1 Tauri, γ Tauri, Aldebaran, θ2 Tauri, 71 Tauri and λ Tauri.[18] Consequently, the Chinese name for ε Tauri itself is 畢宿一 (Bì Xiù yī), "the First Star of Net".[19]
Planetary system
In 2007, a massive exoplanet was reported orbiting the star with a period of 1.6 years in a somewhat eccentric orbit. It was the first planet ever discovered in an open cluster.[2] A 2023 study updated this planet's parameters, and detected additional radial velocity variations that are likely caused by stellar activity.[6]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b (Amateru) | ≥7.190±0.056 MJ | 1.878±0.001 | 585.82+0.26 −0.33 |
0.076+0.009 −0.008 |
— | — |
See also
- Epsilon Tauri in fiction
References
- ↑ 1.0 1.1 1.2 1.3 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940 Gaia DR3 record for this source at VizieR.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Sato, Bun'ei et al. (2007). "A Planetary Companion to the Hyades Giant ε Tauri". The Astrophysical Journal 661 (1): 527–531. doi:10.1086/513503. Bibcode: 2007ApJ...661..527S.
- ↑ "Entry for star HIP 20889". Vizier Catalogue Service. http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=I/311/hip2&recno=20836.
- ↑ Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode: 2018A&A...616A...1G. Gaia DR2 record for this source at VizieR.
- ↑ 5.0 5.1 Böhm-Vitense, Erika et al. (December 2000), "Ultraviolet Emission Lines in BA and Non-BA Giants", The Astrophysical Journal 545 (2): 992–999, doi:10.1086/317850, Bibcode: 2000ApJ...545..992B.
- ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 Teng, Huan-Yu et al. (August 2023). "Revisiting planetary systems in the Okayama Planet Search Program: A new long-period planet, RV astrometry joint analysis, and a multiplicity-metallicity trend around evolved stars". Publications of the Astronomical Society of Japan 75 (6): 1030–1071. doi:10.1093/pasj/psad056. Bibcode: 2023PASJ...75.1030T.
- ↑ 7.0 7.1 Arentoft, T. et al. (February 2019). "Asteroseismology of the Hyades red giant and planet host ɛ Tauri". Astronomy & Astrophysics 622: A190. doi:10.1051/0004-6361/201834690. Bibcode: 2019A&A...622A.190A.
- ↑ "IAU Catalog of Star Names". http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt.
- ↑ "UCAC2 38562433". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=UCAC2+38562433.
- ↑ Flamsteed, John (1725). Historia Coelestis Britannica. H. Meere. p. 47. https://archive.org/details/bub_gb_8q9FAAAAcAAJ.
- ↑ Allen, Richard Hickley (1963). Star Names – Their Lore and Meaning. Dover Books. p. 391. https://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Taurus*.html.
- ↑ "IAU Working Group on Star Names (WGSN)". https://www.iau.org/science/scientific_bodies/working_groups/280/.
- ↑ "Bulletin of the IAU Working Group on Star Names, No. 1". http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf.
- ↑ NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. IAU.org. 9 July 2014
- ↑ "NameExoWorlds The Process". http://nameexoworlds.iau.org/process.
- ↑ Final Results of NameExoWorlds Public Vote Released, International Astronomical Union, 15 December 2015.
- ↑ "NameExoWorlds The Approved Names". http://nameexoworlds.iau.org/names.
- ↑ (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN:978-986-7332-25-7.
- ↑ (in Chinese) 香港太空館 – 研究資源 – 亮星中英對照表 , Hong Kong Space Museum. Accessed on line November 23, 2010.
External links
- "Star Names". Frosty Drew Observatory. http://www.frostydrew.org/observatory/columns/essays/starnames.htm.
- "eps Tau". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=eps+Tau.
Coordinates: 
04h 28m 37.0s, +19° 10′ 49″
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