Epoch J2000 Equinox J2000
|Right ascension||19h 52m 28.36775s|
|Declination||+01° 00′ 20.3696″|
|Apparent magnitude (V)||3.87 (3.5 to 4.4)|
|Spectral type||F6 Ibv|
|U−B color index||+0.51|
|B−V color index||+0.89|
|R−I color index||+0.47|
|Variable type||Cepheid variable|
|Radial velocity (Rv)||–14.8 km/s|
|Proper motion (μ)||RA: +6.91 mas/yr
Dec.: –8.21 mas/yr
|Parallax (π)||2.36 ± 1.04 mas|
|Distance||approx. 1,400 ly
(approx. 400 pc)
|Mass||9.3 ± 0.4 M☉|
|Radius||66 ± 22 R☉|
|Surface gravity (log g)||1.5 cgs|
|Metallicity [Fe/H]||+0.10 dex|
|Age||26.4 ± 3.1 Myr|
Bright Star Catalogue (5th rev. ed.)
Eta Aquilae (η Aql, η Aquilae) is the Bayer designation for a star in the equatorial constellation of Aquila, the eagle. It was once part of the former constellation Antinous. On average, this star has an apparent visual magnitude of 3.87, making it one of the brighter members of Aquila. Based upon parallax measurements made during the Hipparcos mission, this star is located at a distance of roughly 1,382 light-years (424 parsecs), although the parallax estimate has a 44% margin of error.
This is a Cepheid variable star, with an apparent magnitude that ranges from 3.5 to 4.4 over a period of 7.176641 days. Along with Delta Cephei, Zeta Geminorum and Beta Doradus, it is one of the most prominent naked eye Cepheids; that is, both the star itself and the variation in its brightness can be distinguished with the naked eye. Some other Cepheids such as Polaris are bright but have only a very small variation in brightness.
At the relatively young age of 26 million years, this massive star has burned through the hydrogen fuel at its core and evolved into a supergiant, giving it a baseline stellar classification of F6 Ibv. The Ib luminosity class indicates this is a less luminous type of supergiant, while the 'v' suffix shows that the spectrum of the star varies. The periodic pulsations of this star actually cause the stellar class to vary between (F6.5–G2)Ib over the course of each cycle.
Compared to the Sun, Eta Aquilae has around 9 times the mass, roughly 66 times the radius, and is radiating 11,474 times as much luminosity. This energy is being emitted from the outer envelope at an effective temperature of 6,000 K, giving it the yellow-white hued glow of an F-type star. The radius of the star varies by 4.59 × 106 km (0.007 R☉) over the course of a pulsation cycle. Compared to its neighbors, this star has a high peculiar velocity of 16.7 ± 6.9 km s–1.
In Chinese, 天桴 (Tiān Fú), meaning Celestial Drumstick, refers to an asterism consisting of η Aquilae, θ Aquilae, 62 Aquilae and 58 Aquilae. Consequently, η Aquilae itself is known as 天桴四 (Tiān Fú sì, English: the Fourth Star of Celestial Drumstrick.)
This star, along with δ Aql (Denebokab) and θ Aql (Tseen Foo) were Al Mizān (ألميزان), the Scale-beam. According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Mizān were the title for three stars :δ Aql as Al Mizān I,η Aql as Al Mizān II and θ Aql as Al Mizān III.
- van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
- Wielen, R. et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions (35), Astronomisches Rechen-Institut Heidelberg, Bibcode:1999VeARI..35....1W.
- GCVS Query=eta Aql, General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia, retrieved 2010-11-24.
- Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society 410 (1): 190–200, arXiv:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x.
- Nicolet, B. (1978), "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System", Astronomy and Astrophysics Supplement Series 34: 1–49, Bibcode:1978A&AS...34....1N.
- Nordgren, Tyler E. et al. (December 1999), "Stellar Angular Diameters of Late-Type Giants and Supergiants Measured with the Navy Prototype Optical Interferometer", The Astronomical Journal 118 (6): 3032–3038, Bibcode:1999AJ....118.3032N, doi:10.1086/301114.
- Hohle, M. M.; Neuhäuser, R.; Schutz, B. F. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten 331 (4): 349, arXiv:1003.2335, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355.
- Luck, R. E.; Lambert, D. L. (May 1981), "The abundances of carbon, nitrogen, and oxygen in the atmospheres of Cepheid variables - Evidence for helium enrichment", Astrophysical Journal, Part 1 245: 1018–1034, Bibcode:1981ApJ...245.1018L, doi:10.1086/158879.
- Basu, Baidyanath (2003), An Introduction to Astrophysics, PHI Learning Pvt. Ltd., p. 171, ISBN 81-203-1121-3
- Matthews, Keith (December 2008), "A High-Precision Optical Polarimeter to Measure Inclinations of High-Mass X-Ray Binaries", The Publications of the Astronomical Society of the Pacific 120 (874): 1282–1297, arXiv:0810.5561, Bibcode:2008PASP..120.1282W, doi:10.1086/595966.
- Gray, David F.; Stevenson, Kevin B. (April 2007), "Spectroscopic Determination of Radius Changes of Cepheid Variable Stars", The Publications of the Astronomical Society of the Pacific 119 (854): 398–406, Bibcode:2007PASP..119..398G, doi:10.1086/518128
- (Turkish) YILDIZ ADLARI SÖZLÜĞÜ - Mustafa Pultar (Bezek)
- (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.
- (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 3 日
- Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York, NY: Dover Publications Inc, p. 61, ISBN 0-486-21079-0, retrieved 2010-12-12.
- Rhoads, Jack W. (November 15, 1971), Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars, California Institute of Technology: Jet Propulsion Laboratory.
- "HD 187929 -- Classical Cepheid (Delta Cep Type)". SIMBAD Astronomical Database. Retrieved 2007-01-21.
- Eta Aquilae
- Image Eta Aquilae