Epoch J2000.0 Equinox J2000.0
|Right ascension||21h 47m 02.44424s|
|Declination||−16° 07′ 38.2335″|
|Apparent magnitude (V)||2.81|
|Spectral type||A7m III (kA5hF0mF2III)|
|U−B color index||+0.07|
|B−V color index||+0.31|
|Variable type||Eclipsing binary (Algol-type)|
|Radial velocity (Rv)||-6.3 km/s|
|Proper motion (μ)||RA: +261.70 mas/yr
Dec.: -296.70 mas/yr
|Parallax (π)||84.27 ± 0.19 mas|
|Distance||38.70 ± 0.09 ly
(11.87 ± 0.03 pc)
|Period (P)||1.0227683 days|
|Eccentricity (e)||0 (assumed)|
|Periastron epoch (T)||2,448,105.793 ± 0.003 HJD|
|75.3 ± 1.0 km/s|
|δ Cap A|
|Surface gravity (log g)||3.66 cgs|
|Metallicity [Fe/H]||–0.13 dex|
|Rotational velocity (v sin i)||105 km/s|
|δ Cap B|
Delta Capricorni (δ Cap, δ Capricorni), also named Deneb Algedi,is a binary star system approximately 39 light-years away in the constellation of Capricornus (the Sea Goat). The primary star in the system is a white giant star and the combined light of its members makes it the brightest star within the constellation.
Names and cultural associations
It bore the traditional names 'Deneb Algedi', derived from the Arabic ذنب الجدي (ðanab al-jady), meaning "the tail of the goat", referring to the fishlike tail of the celestial sea-goat Capricorn, and Scheddi. According to astrology, Deneb Algedi's representation of a flexible tail is reflected in its association with both good and bad fortune alike. It was one of the fifteen Behenian stars of medieval astrology, associated with chalcedony, marjoram and the kabbalistic symbol . In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN approved the name Deneb Algedi for this star on February 1st, 2017 and it is now so entered in the IAU Catalog of Star Names.
In Chinese astronomy, δ Capricorni is known as 壘壁陣四 (Lěi Bì Zhèn sì), meaning 'The Fourth Star of the Line of Ramparts'. This refers to its presence among an asterism known as 'The Line of Ramparts', which also includes κ Capricorni, ε Capricorni, γ Capricorni, ι Aquarii, λ Aquarii, σ Aquarii, φ Aquarii, 27 Piscium, 29 Piscium, 33 Piscium and 30 Piscium.(Chinese)
Delta Capricorni is an eclipsing binary star system similar to Algol, with an orbital period of 1.022768 days and an inclination close to the line of sight from the Earth. The peak apparent visual magnitude of the pair is 2.81. During an eclipse of the primary, this magnitude drops by 0.24. When the primary is eclipsing the secondary, the magnitude decreases by 0.09.
The primary component, Delta Capricorni A, has an overall stellar classification of A7m III, indicating that it is a giant star that has exhausted the supply of hydrogen at its core. More specifically, this is a chemically-peculiar Am star with a spectral type of kA5hF0mF2 III under the revised MK system. This notation indicates that the K-line matches the temperature of an A5 star, the hydrogen spectral type matches an F0 star, and the metallic absorption lines match an F2 star.
In the past this star was suspected of being a Delta Scuti variable, which is rare for an Am star. This categorization was brought into question during observations in 1994 and it is most likely not inherently variable. Compared to the Sun, the primary has double the mass and nearly twice the radius. It is rotating rapidly with a projected rotational velocity of 105 km s−1. (This rotation rate is synchronous with the orbital period.) Note that it is unusual for an Am star to have such a high rotational velocity. The outer envelope of the star is radiating energy at an effective temperature of 7,301 K, giving it the white-hued glow of an A-type star. The secondary component is a type G or K star with around 90% of the mass of the Sun.
There are two optical companions. A fifteenth magnitude star is one arcminute away, while the thirteenth magnitude star D is over two arcminutes away from the primary star and that distance is increasing.
In 1906 astronomer Vesto Slipher of Lowell Observatory discovered that Delta Capricorni was a spectroscopic binary. The orbit was determined in 1921 by Clifford Crump using 69 radial velocity measurements obtained at Yerkes Observatory. However the eclipsing binary nature of the system was not discovered until 1956 by Olin J. Eggen at Lick Observatory.
- van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv: , Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357
- Malkov, O. Yu.; et al. (February 2006), "A catalogue of eclipsing variables", Astronomy and Astrophysics, 446 (2): 785–789, Bibcode:2006A&A...446..785M, doi:10.1051/0004-6361:20053137
- Gray, R. O.; et al. (October 2003), "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I.", The Astronomical Journal, 126 (4): 2048–2059, arXiv: , Bibcode:2003AJ....126.2048G, doi:10.1086/378365
- Feinstein, A. (November 1974), "Photoelectric UBVRI observations of AM stars", Astronomical Journal, 79: 1290, Bibcode:1974AJ.....79.1290F, doi:10.1086/111675
- Wilson, Ralph Elmer (1953). General Catalogue of Stellar Radial Velocities. Washington: Carnegie Institution of Washington. Bibcode:1953GCRV..C......0W.
- Batten, A. H.; Fletcher, J. M. (April 1992), "A new spectroscopic orbit for Delta Capricorni", Journal of the Royal Astronomical Society of Canada, 86 (2): 99–109, Bibcode:1992JRASC..86...99B
- Trilling, D. E.; et al. (April 2007), "Debris disks in main-sequence binary systems", The Astrophysical Journal, 658 (2): 1264–1288, arXiv: , Bibcode:2007ApJ...658.1289T, doi:10.1086/511668. See p. 33.
- 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 (3): 897–911, arXiv: , Bibcode:2002A&A...393..897R, doi:10.1051/0004-6361:20020943
- "del Cap -- Eclipsing binary of Algol type", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-02-06
- Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv: . Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x.
- Allen, Richard Hinckley (1963). Star Names: Their Lore and Meaning. Dover. p. 141. ISBN 0-486-21079-0. Retrieved 21 June 2015.
- Bakich, Michael E (1995). The Cambridge Guide to the Constellations. Cambridge University Press. p. 116. ISBN 0-521-44921-9. Retrieved 21 June 2015.
- Wright, Anne (2003), The Fixed Stars: Deneb Algedi, archived from the original on June 16, 2005, retrieved July 28, 2005
- "International Astronomical Union | IAU". www.iau.org. Retrieved 2017-04-01.
- 香港太空館 - 研究資源 - 亮星中英對照表 Archived September 29, 2009, at the Wayback Machine., Hong Kong Space Museum. Accessed on line November 23, 2010.
- (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.
- Lloyd, C.; Wonnacott, D. (January 1994), "Is the ROSAT Wide Field Camera EUV source and AM eclipsing binary, Delta Capricorni, also a Delta Scuti variable?", Monthly Notices of the Royal Astronomical Society, 266: L13–L16, Bibcode:1994MNRAS.266L..13L, doi:10.1093/mnras/266.1.l13
- "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-10, retrieved 2012-01-16
- Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
- Slipher, V. M. (1906). "Variable radial velocity of delta Capricorni". The Astrophysical Journal. 24: 361. Bibcode:1906ApJ....24..361S. doi:10.1086/141403.
- Crump, C. C. (1921). "The orbit of 49 delta Capricorni". The Astrophysical Journal. 54: 127–132. Bibcode:1921ApJ....54..127C. doi:10.1086/142630.
- Eggen, Olin J. (1956). "Two New Bright Variable Stars: δ Delphini and δ Capricorni". Publications of the Astronomical Society of the Pacific. 68 (405): 541–544. Bibcode:1956PASP...68..541E. doi:10.1086/126996.
- Malasan, H. L.; et al. (1989). "Delta Capricorni – an evolved binary or a main-sequence binary?". Astronomical Journal. 97: 499–504. Bibcode:1989AJ.....97..499M. doi:10.1086/114999.