Theta Aquilae

Theta Aquilae (θ Aql, θ Aquilae) is a binary star in the constellation Aquila. The combined apparent visual magnitude of the pair is 3.26,[2] making it the fourth-brightest member of the constellation. In Chinese, it has the traditional name Tseen Foo /ˌsiːn ˈfuː/, from the Chinese 天桴 (Mandarin pronunciation tiānfú), which could mean "heavenly raft" or "heavenly ridgepole"; it might also mean "heavenly drumsticks", with Altair, Beta Aquilae and Gamma Aquilae being the drum. This distance to this star can be determined through the parallax technique, yielding an estimate of roughly 286 light-years (88 parsecs) from Earth.[1]

Theta Aquilae
Location of θ Aquilae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquila
Right ascension 20h 11m 18.28528s[1]
Declination –00° 49′ 17.2626″[1]
Apparent magnitude (V) 3.26[2]
Characteristics
Spectral type B9.5 III + B9.5 III[3]
U−B color index –0.15[2]
B−V color index –0.07[2]
Astrometry
Radial velocity (Rv)–27.3[4] km/s
Proper motion (μ) RA: +35.26[1] mas/yr
Dec.: +5.71[1] mas/yr
Parallax (π)11.39 ± 0.24 mas[1]
Distance286 ± 6 ly
(88 ± 2 pc)
Absolute magnitude (MV)–1.39/0.14[5]
Orbit[6]
Period (P)17.124281 ± 0.000038 days
Semi-major axis (a)3.148 ± 0.002 mas″
Eccentricity (e)0.6040 ± 0.0009
Inclination (i)144.10 ± 0.18°
Longitude of the node (Ω)96.92 ± 0.19°
Periastron epoch (T)JD 2458624.154 ± 0.004
Argument of periastron (ω)
(primary)		33.73 ± 0.22°
Semi-amplitude (K1)
(primary)		48.78 ± 0.09 km/s
Semi-amplitude (K2)
(secondary)		63.48 ± 0.11 km/s
Details
θ Aql A
Mass3.564 ± 0.049[6] M☉
Radius4.76 ± 0.14[6] R☉
Luminosity229.8 ± 22.5[6] L☉
Surface gravity (log g)3.64 ± 0.02[6] cgs
Temperature10300 ± 200[6] K
Metallicity [Fe/H]+0.20[7] dex
Rotational velocity (v sin i)36.3 ± 0.4[6] km/s
Age20.9[5] Myr
θ Aql B
Mass2.739 ± 0.037[6] M☉
Radius2.34 ± 0.07[6] R☉
Luminosity54.0 ± 5.8[6] L☉
Surface gravity (log g)4.14 ± 0.02[6] cgs
Temperature10230 ± 220[6] K
Rotational velocity (v sin i)13.6 ± 0.9[6] km/s
Other designations
Tseen Foo, 65 Aql, BD–01 3911, FK5 756, HD 191692, HIP 99473, HR 7710, SAO 144150.
Database references
SIMBADdata

Properties

Theta Aquilae is a double-lined spectroscopic binary,[8] which indicates that the individual components have not been viewed through a telescope; instead, what can be viewed is their combined spectrum with the individual absorption line features shifting back and forth over the course of an orbit because of the Doppler effect. Their orbit has a period of 17.1 days with a large orbital eccentricity is 0.60. At the estimated distance of this system, the angular separation of 3.2[5] milliarcseconds corresponds to a physical separation of only about 0.24–0.28 astronomical units.[9]

Both stars have a matching stellar classification of B9.5 III,[3] indicating that they are massive, B-type giant stars that have exhausted the supply of hydrogen at their cores and evolved away from the main sequence of stars like the Sun. Hummel et al. (1996) gave the primary component, θ Aql A, an estimated mass of 3.6 solar, a radius 4.8 the Sun's, and 278 the luminosity of the Sun. For the secondary component, θ Aql B, they give the corresponding parameters as 2.9 times the mass, 2.4 times the radius and 68 times the luminosity of the Sun.[5] Based upon their estimated parameters, Kaler (2008) suggests that θ Aql A is actually a subgiant star, while θ Aql B is a main sequence star.[9]

Etymology

In Chinese, 天桴 (Tiān Fú), meaning Celestial Drumstick, refers to an asterism consisting of θ Aquilae, 62 Aquilae, 58 Aquilae and η Aquilae.[10] Consequently, the Chinese name for θ Aquilae itself is 天桴一 (Tiān Fú yī, English: the First Star of Celestial Drumstick.)[11]

In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Thanih Ras al Akab (تاني ألرأس ألعقاب - taanii al ra’s alʕuqāb), which was translated into Latin as Secunda Capitis Vulturis, meaning the second (star) of eagle's head.[12]

This star, along with δ Aql and η Aql, were Al Mizān (ألميزان), the Scale-beam.[13] 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.[14]

This star, together with η Aql, δ Aql, ι Aql, κ Aql and λ Aql, constituted the obsolete constellation Antinous.[15]

References
  1. 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, S2CID 18759600.
  2. Cowley, A.; et al. (April 1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819.
  3. Cunha, M. S.; et al. (November 2007), "Asteroseismology and interferometry", The Astronomy and Astrophysics Review, 14 (3–4): 217–360, arXiv:0709.4613, Bibcode:2007A&ARv..14..217C, doi:10.1007/s00159-007-0007-0, S2CID 16590095.
  4. Wilson, R. E. (1953), "General Catalogue of Stellar Radial Velocities", Washington, Carnegie Institute of Washington D.C., Bibcode:1953GCRV..C......0W.
  5. Hummel, C. A.; et al. (July 1995), "Orbits of Small Angular Scale Binaries Resolved with the Mark III Interferometer", Astronomical Journal, 110: 376, Bibcode:1995AJ....110..376H, doi:10.1086/117528.
  6. Lester, Kathryn V.; Schaefer, Gail H.; Fekel, Francis C.; Gies, Douglas R.; Henry, Todd J.; Jao, Wei-Chun; Paredes, Leonardo A.; Hubbard-James, Hodari-Sadiki; Farrington, Christopher D.; Gordon, Kathryn D.; Chojnowski, S. Drew; Monnier, John D.; Kraus, Stefan; Bouquin, Jean-Baptiste Le; Anugu, Narsireddy; Brummelaar, Theo Ten; Davies, Claire L.; Gardner, Tyler; Labdon, Aaron; Lanthermann, Cyprien; Setterholm, Benjamin R. (2022). "Visual Orbits of Spectroscopic Binaries with the CHARA Array. IV. HD 61859, HD 89822, HD 109510, and HD 191692". The Astronomical Journal. 164 (6): 228. arXiv:2209.09993. Bibcode:2022AJ....164..228L. doi:10.3847/1538-3881/ac9385. S2CID 252408703.
  7. Adelman, S. J.; Nasson, M. A. (June 1980), "Abundance analyses of Theta Aquilae /B9.5 III/, Nu Capricorni /B9.5 V/, and Sigma Aquarii /AO IVs/", Publications of the Astronomical Society of the Pacific, 92: 346–356, Bibcode:1980PASP...92..346A, doi:10.1086/130675.
  8. van Rensbergen, W.; De Loore, C.; Jansen, K. (February 2006), "Evolution of interacting binaries with a B type primary at birth", Astronomy and Astrophysics, 446 (3): 1071–1079, Bibcode:2006A&A...446.1071V, doi:10.1051/0004-6361:20053543.
  9. Kaler, James B. (September 19, 2008), "THETA AQL (Theta Aquilae)", Stars, University of Illinois, retrieved 2012-02-19.
  10. (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.
  11. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 3 日
  12. 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.
  13. Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York: Dover Publications Inc., p. 61, ISBN 0-486-21079-0, retrieved 2010-12-12.
  14. Rhoads, Jack W. (November 15, 1971), Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars (PDF), Jet Propulsion Laboratory, California Institute of Technology.
  15. Ian Ridpath's Star Tales - Antinous
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