Theta Aquilae

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Theta Aquilae
Diagram showing star positions and boundaries of the Aquila constellation and its surroundings
Cercle rouge 100%.svg

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[1] mas
Distance 286 ± 6 ly
(88 ± 2 pc)
Absolute magnitude (MV) –1.39/0.14[5]
Orbit[5]
Period (P) 17.122 ± 0.001 days
Semi-major axis (a) 3.2 ± 0.1"
Eccentricity (e) 0.60 ± 0.02
Inclination (i) 143.5 ± 3.0°
Longitude of the node (Ω) 99 ± 5°
Periastron epoch (T) 7801.7 ± 0.1
Argument of periastron (ω)
(secondary)
215 ± 10°
Details
θ Aql A
Mass 3.6 ± 0.8[5] M
Radius 4.8 ± 0.5[5] R
Luminosity 278 ± 54[5] L
Surface gravity (log g) 3.3[6] cgs
Temperature 10,286[6] K
Metallicity [Fe/H] +0.20[6] dex
Rotational velocity (v sin i) 53[7] km/s
Age 20.9[5] Myr
θ Aql B
Mass 2.9 ± 0.6[5] M
Radius 2.4 ± 0.2[5] R
Luminosity 68 ± 14[5] L
Other designations
Tseen Foo, 65 Aql, BD–01 3911, FK5 756, HD 191692, HIP 99473, HR 7710, SAO 144150.
Database references
SIMBAD data

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, which is derived from the Mandarin 天桴 tiānfú meaning "the heavenly raft(er)"; it may also mean 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]

Properties[edit]

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[edit]

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, θ Aquilae itself is known as 天桴一 (Tiān Fú yī, English: the First Star of Celestial Drumstrick.)[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 (Denebokab) 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 l Mizān II and θ Aql as Al Mizān III.[14]

References[edit]

  1. ^ a b c d e f 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. 
  2. ^ a b c d 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. ^ a b 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. 
  4. ^ Wilson, R. E. (1953), General Catalogue of Stellar Radial Velocities, Carnegie Institute of Washington D.C., Bibcode:1953GCRV..C......0W. 
  5. ^ a b c d e f g h i j k 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. ^ a b c 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. 
  7. ^ Royer, F. et al. (October 2002), Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i, Astronomy and Astrophysics 393: 897–911, arXiv:astro-ph/0205255, Bibcode:2002A&A...393..897R, doi:10.1051/0004-6361:20020943. 
  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. ^ a b Kaler, James B. (September 19, 2008), THETA AQL (Theta Aquilae), Stars (University of Illinois), retrieved 2012-02-19. 
  10. ^ (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. ^ (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: 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, Jet Propulsion Laboratory, California Institute of Technology. 

External links[edit]