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Eta Aquilae

Eta Aquilae (η Aql, η Aquilae) is a multiple star in the equatorial constellation of Aquila, the eagle. It was once part of the former constellation Antinous. Its apparent visual magnitude varies between 3.49 and 4.3,[3] making it one of the brighter members of Aquila. Based upon parallax measurements made by the Gaia spacecraft on its third data release (DR3), this star is located at a distance of roughly 272 parsecs (890 light-years).[1] The primary component is a Classical Cepheid variable.[7]

η Aquilae
Location of η Aql (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquila
Right ascension 19h 52m 28.3689s[1]
Declination +01° 00′ 20.372″[1]
Apparent magnitude (V) 3.87[2] (3.49 – 4.3[3])
Characteristics
Spectral type F6 Iab[4] (or F6Ib–G4Ib[3]) + B9.8 V[4] + F1-5 V[5]
U−B color index +0.51[6]
B−V color index +0.89[6]
Variable type δ Cep[7]
Astrometry
Radial velocity (Rv)10.82±0.55[1] km/s
Proper motion (μ) RA: +8.89 mas/yr[1]
Dec.: –8.322 mas/yr[1]
Parallax (π)3.6715 ± 0.1942 mas[1]
Distance885.4+41.7
−45 ly
(271.6+12.8
−13.8 pc)[8]
Absolute magnitude (MV)−3.70[4]
Details
A
Mass4.24±0.58;[9] 5.7;[4] 6.15;[1] M☉
Radius59±2[10] R☉
Luminosity3,368±195[10] L☉
Surface gravity (log g)1.834[11] cgs
Temperature5,747±19[10] K
Metallicity [Fe/H]–0.19[1] dex
Age150±50[9] Myr
B
Mass2.3[4] M☉
Other designations
55 Aquilae, BD+00°4337, FK5 746, HD 187929, HIP 97804, HR 7570, SAO 125159, AAVSO 1947+00, 2MASS J19522835+0100203
Database references
SIMBADdata

System

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The η Aquilae system contains at least two stars, probably three. The primary star η Aql A is by far the brightest and dominates the spectrum. An ultraviolet excess in the spectral energy distribution suggest the presence of a faint hot companion, η Aql B, which has been given a spectral type of B8.9 V. The fractional spectral type is an artefact of the mathematics used to model the spectrum, not an indication of any specific spectral features that would be intermediate between B8 and B9.[4] Radial velocity measurements could not find a satisfactory fit, which suggests that the orbit of η Aql B may be face-on, or very large.[12]

A companion has been resolved visually 0.66" distant, but measurements give this a spectral type of F1 - F5. It seems likely that the hot star detected in the spectrum is closer and unresolved. The resolved companion has not been shown to be physically associated, but it is estimated that it would have a period of nearly a thousand years. Measurements with the HST fine guidance sensors show variations likely to be due to orbital motion on a scale of two years, so η Aql would appear to be a triple system.[4][5]

At Eta Aquilae's distance (272 pc), its apparent brightness is diminished by 0.74 magnitudes due to extinction caused by interstellar dust between Earth and the star.[1]

Cepheid variable

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A visual band light curve for η Aquilae, adapted from Kiss (1998)[13]

η Aquilae A is a Cepheid variable star, discovered by Edward Pigott in 1784.[14][3] It has an apparent magnitude that ranges from 3.49 to 4.3 over a period of 7.177 days.[3] Along with Delta Cephei, Zeta Geminorum and Beta Doradus, it is one of the most prominent naked eye Cepheids;[15] 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.

This massive star, being 100–200 million years old,[9] has burned through the hydrogen fuel at its core and evolved into a supergiant, giving it a baseline stellar classification of F6 Iab.[4] The periodic pulsations of this star actually cause the stellar class to vary between F6.5Ib to G2Ib over the course of each cycle.[16]

Compared to the Sun, Eta Aquilae has around 6 times the mass,[4] 60 times the radius, and is radiating 3,400 times as much luminosity.[10] This energy is being emitted from the outer envelope at an effective temperature of 5,700 K,[10] giving it the yellow-whitish hued glow of a G-type star. The radius of the star varies by 4.59 × 106 km (0.007 R☉) over the course of a pulsation cycle.[17] Compared to its neighbors, this star has a high peculiar velocity of 16.7 ± 6.9 km s−1.[18]

Name

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In Chinese, 天桴 (Tiān Fú), meaning Celestial Drumstick, refers to an asterism consisting of η Aquilae, θ Aquilae, 62 Aquilae and 58 Aquilae.[19] Consequently, the Chinese name for η Aquilae itself is 天桴四 (Tiān Fú sì, English: the Fourth Star of Celestial Drumstick.)[20]

This star, along with δ Aql and θ Aql, were Al Mizān (ألميزان), the Scale-beam.[21]According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Mizān was the title for three stars: δ Aql as Al Mizān I, η Aql as Al Mizān II and θ Aql as Al Mizān III.[22]

η Aquilae, together with θ Aql, δ Aql, ι Aql, κ Aql and λ Aql, was part of the obsolete constellation Antinous.[23]

Notes

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References

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  1. ^ a b c d e f g h i Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. ^ Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb, 35 (35): 1, Bibcode:1999VeARI..35....1W.
  3. ^ a b c d e "VSX : Detail for eta Aql". AAVSO. Retrieved 2024-05-25.
  4. ^ a b c d e f g h i Remage Evans, Nancy; Bond, Howard E.; Schaefer, Gail H.; Mason, Brian D.; Karovska, Margarita; Tingle, Evan (2013). "Binary Cepheids: Separations and Mass Ratios in 5 M ⊙ Binaries". The Astronomical Journal. 146 (4): 93. arXiv:1307.7123. Bibcode:2013AJ....146...93E. doi:10.1088/0004-6256/146/4/93. S2CID 34133110.
  5. ^ a b Gallenne, A.; Kervella, P.; Mérand, A.; Evans, N. R.; Girard, J. H. V.; Gieren, W.; Pietrzyński, G. (2014). "Searching for visual companions of close Cepheids". Astronomy & Astrophysics. 567: A60. arXiv:1406.0493. Bibcode:2014A&A...567A..60G. doi:10.1051/0004-6361/201423872. S2CID 55702630.
  6. ^ a b 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.
  7. ^ a b GCVS Query=eta Aql, General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia, retrieved 2010-11-24.
  8. ^ Bailer-Jones, C. A. L.; Rybizki, J.; Fouesneau, M.; Demleitner, M.; Andrae, R. (2021-03-01). "Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3". The Astronomical Journal. 161 (3): 147. arXiv:2012.05220. Bibcode:2021AJ....161..147B. doi:10.3847/1538-3881/abd806. ISSN 0004-6256. Data about this star can be seen here.
  9. ^ a b c Baines, Ellyn K.; Armstrong, J. Thomas; Schmitt, Henrique R.; Zavala, R. T.; Benson, James A.; Hutter, Donald J.; Tycner, Christopher; Van Belle, Gerard T. (2018), "Fundamental Parameters of 87 Stars from the Navy Precision Optical Interferometer", The Astronomical Journal, 155 (1): 30, arXiv:1712.08109, Bibcode:2018AJ....155...30B, doi:10.3847/1538-3881/aa9d8b, S2CID 119427037.
  10. ^ a b c d e Gallenne, A.; Mérand, A.; Kervella, P.; Pietrzyński, G.; Gieren, W.; Hocdé, V.; Breuval, L.; Nardetto, N.; Lagadec, E. (May 25, 2021). "Extended envelopes around Galactic Cepheids. V. Multi-wavelength and time-dependent analysis of IR excess". Astronomy & Astrophysics. 651: A113. arXiv:2105.12197. Bibcode:2021A&A...651A.113G. doi:10.1051/0004-6361/202140350. ISSN 0004-6361.
  11. ^ Groenewegen, M. A. T. (2020-03-01). "Analysing the spectral energy distributions of Galactic classical Cepheids". Astronomy and Astrophysics. 635: A33. arXiv:2002.02186. Bibcode:2020A&A...635A..33G. doi:10.1051/0004-6361/201937060. ISSN 0004-6361. Eta Aquilae's database entry at VizieR.
  12. ^ Benedict, G. Fritz; Barnes, Thomas G.; Evans, Nancy R.; Cochran, William D.; Anderson, Richard I.; McArthur, Barbara E.; Harrison, Thomas E. (2022). "The η Aquilae System: Radial Velocities and Astrometry in Search of η Aql B". The Astronomical Journal. 163 (6): 282. arXiv:2204.09759. Bibcode:2022AJ....163..282B. doi:10.3847/1538-3881/ac68ed. S2CID 248299714.
  13. ^ Kiss, Laszlo L. (July 1998). "A photometric and spectroscopic study of the brightest northern Cepheids - I. Observations". Monthly Notices of the Royal Astronomical Society. 297 (3): 825. Bibcode:1998MNRAS.297..825K. doi:10.1046/j.1365-8711.1998.01559.x. S2CID 121699816.
  14. ^ Pigott, Edward (1785). "Observations of a New Variable Star. In a Letter from Edward Pigott, Esq. to Sir H. C. Englefield, Bart. F. R. S. and A. S.". Philosophical Transactions of the Royal Society of London. 75: 127–136. Bibcode:1785RSPT...75..127P. doi:10.1098/rstl.1785.0007. S2CID 186212958.
  15. ^ Basu, Baidyanath (2003), An Introduction to Astrophysics, PHI Learning Pvt. Ltd., p. 171, ISBN 978-81-203-1121-3
  16. ^ Wiktorowicz, Sloane J.; 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, S2CID 14883175.
  17. ^ 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, CiteSeerX 10.1.1.495.3147, doi:10.1086/518128
  18. ^ 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, S2CID 118629873.
  19. ^ Ian Ridpath's Star Tales - Aquila
  20. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 3 日 Archived 2011-05-21 at the Wayback Machine
  21. ^ Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York, NY: Dover Publications Inc., p. 61, ISBN 978-0-486-21079-7, retrieved 2010-12-12.
  22. ^ Rhoads, Jack W. (November 15, 1971), Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars (PDF), California Institute of Technology: Jet Propulsion Laboratory.
  23. ^ Ian Ridpath's Star Tales - Antinous
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