Epoch J2000 Equinox J2000
|Right ascension||13h 54m 41.07892s|
|Declination||+18° 23′ 51.7946″|
|Apparent magnitude (V)||2.680|
|Spectral type||G0 IV|
|U−B color index||+0.207|
|B−V color index||+0.585|
|Radial velocity (Rv)||-1.6 km/s|
|Proper motion (μ)|| RA: -60.95 mas/yr |
Dec.: -356.29 mas/yr
|Parallax (π)||87.75 ± 1.24 mas|
|Distance||37.2 ± 0.5 ly |
(11.4 ± 0.2 pc)
|Absolute magnitude (MV)||2.41|
|Mass||1.71 ± 0.05 M☉|
|Radius||2.672 ± 0.028 R☉|
|Luminosity||8.89 ± 0.16 L☉|
|Surface gravity (log g)||3.817 ± 0.015 cgs|
|Temperature||6,100 ± 28 K|
|Metallicity [Fe/H]||+0.27 dex|
|Rotational velocity (v sin i)||11.8 km/s|
Eta Boötis (η Boötis, abbreviated Eta Boo, η Boo) is a binary star in the constellation of Boötes. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 37 light-years (11 parsecs) distant from the Sun. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. It forms a double star with the star BD+19 2726.
As a constituent of a double pair, Eta Boötis is also designated WDS J13547+1824A, with its two components being designated Aa (also named Muphrid) and Ab. (As part of a binary pair, they are also designated Eta Boötis A and B, respectively.) BD +19 2726 is also designated WDS J13547+1824B.
η Boötis (Latinised to Eta Boötis) is the binary pair's Bayer designation; η Boötis A and B those of its two components. The designations of the two constituents of the double pair as WDS J13547+1824A and B and those of A's components - Aa and Ab - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).
Eta Boötis bore the traditional names Muphrid and Saak. Muphrid is from the Arabic مفرد الرامح mufrid ar-rāmiħ "the (single) one of the lancer". In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems. It approved the name Muphrid for the component WDS J13547+1824Aa (Eta Boötis A) on 12 September 2016 and it is now so included in the List of IAU-approved Star Names.
In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Ramih al Ramih (رمح الرامح rumḥ al rāmiḥ), which was translated into Latin as Lancea Lanceator, possibly meaning the lance of the lancer.
In Chinese, 右攝提 (Yòu Niè Dī), meaning "the Right Conductor", refers to an asterism consisting of Eta Boötis, Tau Boötis and Upsilon Boötis. Consequently, Eta Boötis itself is known as 右攝提一 (Yòu Niè Dī yī, English: "the First Star of the Right Conductor").
Eta Boötis is a suspected spectroscopic binary with a reported period of 494 days, but the companion was not confirmed through speckle interferometry. This measurement does not rule out a low mass stellar companion of spectral class M7.
Eta Boötis presents as a subgiant that has begun the process of evolving from a main sequence star into a red giant. It has about 1.7 times the mass of the Sun and 2.7 times the Sun's radius. The estimated age of this star is about 2.7 billion years. Based on its spectra, it has a significant excess of elements heavier than helium. In fact the ratio of iron to hydrogen is considered close to the upper limit for dwarf stars in the galactic disk.
Eta Boötis appears close to the prominent star Arcturus (Alpha Bootis) in Earth's sky, and Arcturus is in fact its closest stellar neighbor, as both stars are nearly identical in distance from the Sun. The two stars are about 3.24 light-years apart, and each would appear bright in the other's sky. Arcturus would appear as roughly magnitude -5.2 (about 120 times brighter than it appears from Earth, or close to twice the brightness of Venus) in the night sky of a hypothetical planet orbiting Eta Boötis, while Eta Boötis would appear at about magnitude −2.4 (absolute magnitude −2.41 at 0.99 parsec) in the sky of a hypothetical planet orbiting Arcturus, or over twice the brightness of Sirius in the night sky.
- 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.
- Holmberg, J.; Nordström, B.; Andersen, J. (July 2009), "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics", Astronomy and Astrophysics, 501 (3): 941–947, arXiv:0811.3982, Bibcode:2009A&A...501..941H, doi:10.1051/0004-6361/200811191
- Thévenin, F.; et al. (June 2005), "VLTI/VINCI diameter constraints on the evolutionary status of δ Eri, ξ Hya, η Boo", Astronomy and Astrophysics, 436 (1): 253–262, arXiv:astro-ph/0501420, Bibcode:2005A&A...436..253T, doi:10.1051/0004-6361:20042075
- Oja, T., "UBV photometry of stars whose positions are accurately known. III", Astronomy and Astrophysics Supplement Series, 65 (2): 405–4
- van Belle, Gerard T.; Ciardi, David R.; Boden, Andrew F. (March 2007), "Measurement of the Surface Gravity of η Bootis", The Astrophysical Journal, 657 (2): 1058–1063, arXiv:astro-ph/0701120, Bibcode:2007ApJ...657.1058V, doi:10.1086/510830
- Schröder, C.; Reiners, A.; Schmitt, J. H. M. M. (January 2009), "Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo" (PDF), Astronomy and Astrophysics, 493 (3): 1099–1107, Bibcode:2009A&A...493.1099S, doi:10.1051/0004-6361:200810377
- 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
- "Washington Double Star Catalog". United States Naval Observatory. Retrieved 2 January 2018.
- "Naming Stars". IAU.org. Retrieved 16 December 2017.
- Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
- Rumrill, H. B. (June 1936), "Star Name Pronunciation", Publications of the Astronomical Society of the Pacific, 48 (283): 139–154, 150, Bibcode:1936PASP...48..139R, doi:10.1086/124681
- Cannon, Garland Hampton (1994), The Arabic contributions to the English language: an historical dictionary, Otto Harrassowitz Verlag, p. 264, ISBN 978-3-447-03491-3
- IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
- "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
- Knobel, E. B. (June 1895), "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket", Monthly Notices of the Royal Astronomical Society, 55 (8): 429, Bibcode:1895MNRAS..55..429K, doi:10.1093/mnras/55.8.429
- (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 Archived January 30, 2011, at the Wayback Machine., Hong Kong Space Museum. Accessed on line November 23, 2010.
- Bensby, T.; Zenn, A. R.; Oey, M. S.; Feltzing, S. (2007). "Tracing the Galactic Thick Disk to Solar Metallicities". The Astrophysical Journal. 663 (1): L13. arXiv:0705.2060. Bibcode:2007ApJ...663L..13B. doi:10.1086/519792.