Delta Cygni
  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 19h 44m 58.47854s[1] |
| Declination | +45° 07′ 50.9161″[1] |
| Apparent magnitude (V) | 2.87[2] |
| Characteristics | |
| Spectral type | A0 IV[3] (B9 III + F1 V[4]) |
| U−B color index | −0.10[5] |
| B−V color index | −0.02[5] |
| Variable type | Suspected[6] |
| Astrometry | |
| Radial velocity (Rv) | −20.1[7] km/s |
| Proper motion (μ) | RA: +44.07[1] mas/yr Dec.: +48.66[1] mas/yr |
| Parallax (π) | 19.77±0.48 mas[1] |
| Distance | 165 ± 4 ly (51 ± 1 pc) |
| Absolute magnitude (MV) | −0.74[8] |
| Orbit[9] | |
| Primary | A |
| Companion | B |
| Period (P) | 780.27 yr |
| Semi-major axis (a) | 3.0″ |
| Eccentricity (e) | 0.4670 |
| Details[10] | |
| Mass | 2.93 M☉ |
| Radius | 4.81±0.36[11] R☉ |
| Luminosity | 155 L☉ |
| Surface gravity (log g) | 3.4±0.25[11] cgs |
| Temperature | 10400±400[11] K |
| Rotational velocity (v sin i) | 142[11] km/s |
| Other designations | |
| Fawaris, δ Cyg, 18 Cygni, 18 Cyg, BD+44°3234, HD 186882, HIP 97165, HR 7528, SAO 48796, WDS J19450+4508AB | |
| Database references | |
| SIMBAD | data |
Delta Cygni is a binary star of a combined third-magnitude in the constellation of Cygnus. It is also part of the Northern Cross asterism whose brightest star is Deneb. Its name is a Bayer designation that is Latinized from δ Cygni, and abbreviated Delta Cyg or δ Cyg. Based upon parallax measurements obtained during the Hipparcos mission, Delta Cygni is located roughly 165 light-years (51 parsecs) distant from the Sun.[1]
Delta Cygni's two components are designated Delta Cygni A (officially named Fawaris /fəˈwɛərɪs/)[12] and B. More widely separated is a faint third component, a 12th magnitude star that is moving along with the others. Together they form a triple star system.[13]
Nomenclature
[edit]δ Cygni (Latinised to Delta Cygni) is the binary's Bayer designation. The designations of the two components as Delta Cygni A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[14]
Traditionally, Delta Cygni had no proper name.[13] It belonged to the Arabic asterism al-Fawāris (الفوارس), meaning "the Riders" in indigenous Arabic,[15] together with Zeta, Epsilon, and Gamma Cygni, the transverse of the Northern Cross. In 2016, the IAU organized a Working Group on Star Names (WGSN)[16] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[17] It approved the name Fawaris for the component Delta Cygni A on 1 June 2018 and it is now so included in the List of IAU-approved Star Names.[12]
In Chinese, 天津 (Tiān Jīn), meaning Celestial Ford, refers to an asterism consisting of Delta Cygni, Gamma Cygni, 30 Cygni, Alpha Cygni (Deneb) and Nu, Tau, Upsilon, Zeta and Epsilon Cygni.[18] Consequently, the Chinese name for Delta Cygni itself is 天津二 (Tiān Jīn èr, English: the Second Star of Celestial Ford).[19]
Properties
[edit]The primary, Delta Cygni A, is a blue-white giant star of spectral class B9,[4] with a temperature of 10,400 K.[11] It is nearing the end of its main-sequence life stage with a luminosity 155 times that of the Sun,[10] a radius of 4.81 solar radii,[11] and a mass approximately 2.93 solar masses. Like many hot stars, it spins rapidly, at least 135 kilometers per second at the equator, about 60 times that of the Sun.[10]
The close companion Delta Cygni B is a yellow-white F-type main-sequence star of the sixth magnitude (6.33) with a luminosity about 6 times that of the Sun, and a mass about 1.5 times the Sun's. The two stars orbit each other at an average distance of 157 AU and a period of 780 years.[13]
The much more distant third companion is an orange (class K) twelfth magnitude star, and only two thirds as massive.[13]
The two main stars together appear with a spectral type of A0 IV.[3] As seen from Earth, the entire triple star system of Delta Cygni shines at a combined apparent magnitude of 2.87.[2] Both δ Cygni A and B have been suspected to vary in brightness. δ Cygni A was reported in 1951 as varying between magnitudes 2.85 and 2.89, and δ Cygni B was reported in 1837 to vary between magnitudes 6.3 and 8.5. The variability of the stars has not been confirmed.[6]
Pole Star
[edit]Delta Cygni is a visible star located within 3° of the precessional path traced across the celestial sphere by the Earth's North pole. For at least four centuries around 11,250 AD it will probably be considered a pole star, a title currently held by Polaris which is just 0.5° off of the precessional path.
| Preceded by | Pole Star | Succeeded by |
|---|---|---|
| Deneb | ~11,000 AD to ~11,500 AD |
Vega |
References
[edit]- ^ 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. S2CID 18759600.
- ^ a b Malagnini, M. L.; Morossi, C. (November 1990). "Accurate absolute luminosities, effective temperatures, radii, masses and surface gravities for a selected sample of field stars". Astronomy and Astrophysics Supplement Series. 85 (3): 1015–1019. Bibcode:1990A&AS...85.1015M.
- ^ a b Zorec, J.; et al. (July 2009). "Fundamental parameters of B supergiants from the BCD system. I. Calibration of the (λ_1, D) parameters into Teff". Astronomy and Astrophysics. 501 (1): 297–320. arXiv:0903.5134. Bibcode:2009A&A...501..297Z. doi:10.1051/0004-6361/200811147. S2CID 14969137.
- ^ a b Edwards, T. W. (April 1976). "MK classification for visual binary components". Astronomical Journal. 81: 245–249. Bibcode:1976AJ.....81..245E. doi:10.1086/111879.
- ^ a b Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99): 99. Bibcode:1966CoLPL...4...99J.
- ^ a b Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1: B/gcvs. Bibcode:2009yCat....102025S.
- ^ Evans, D. S. (June 20–24, 1966). Batten, Alan Henry; Heard, John Frederick (eds.). "The Revision of the General Catalogue of Radial Velocities". Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30. 30: 57. Bibcode:1967IAUS...30...57E.
- ^ Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
- ^ Malkov, O. Yu.; et al. (October 2012). "Dynamical masses of a selected sample of orbital binaries". Astronomy & Astrophysics. 546: 5. Bibcode:2012A&A...546A..69M. doi:10.1051/0004-6361/201219774. A69.
- ^ a b c Challouf, M.; et al. (2014). "Improving the surface brightness-color relation for early-type stars using optical interferometry⋆". Astronomy & Astrophysics. 570: A104. arXiv:1409.1351. Bibcode:2014A&A...570A.104C. doi:10.1051/0004-6361/201423772. S2CID 14624307.
- ^ a b c d e f Gordon, Kathryn D.; Gies, Douglas R.; Schaefer, Gail H.; Huber, Daniel; Ireland, Michael (2019). "Angular Sizes, Radii, and Effective Temperatures of B-type Stars from Optical Interferometry with the CHARA Array". The Astrophysical Journal. 873 (1): 91. Bibcode:2019ApJ...873...91G. doi:10.3847/1538-4357/ab04b2. S2CID 125181833.
- ^ a b "Naming Stars". IAU.org. Retrieved 18 June 2018.
- ^ a b c d Kaler, James B. "Delta Cygni". Stars. University of Illinois. Retrieved 2018-10-03.
- ^ 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].
- ^ Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York, NY: Dover Publications Inc. pp. 193, 197. ISBN 978-0-486-21079-7.
{{cite book}}: ISBN / Date incompatibility (help) - ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
- ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
- ^ (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) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 4 日 Archived 2011-05-22 at the Wayback Machine