Delta Cassiopeiae

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δ Cassiopeiae
Cassiopeia constellation map.svg
Red circle.svg

Location of δ Cassiopeiae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Cassiopeia
Right ascension 01h 25m 48.95147s[1]
Declination +60° 14′ 07.0225″[1]
Apparent magnitude (V) 2.68[2]
Spectral type A5 IV[3]
U−B color index +0.13[2]
B−V color index +0.13[2]
Variable type Algol[4]
Radial velocity (Rv) −6.7[5] km/s
Proper motion (μ) RA: 296.57[1] mas/yr
Dec.: –49.22[1] mas/yr
Parallax (π) 32.81 ± 0.14[1] mas
Distance 99.4 ± 0.4 ly
(30.5 ± 0.1 pc)
Absolute magnitude (MV) +0.28[6]
Mass 2.49[7] M
Radius 3.90[8] R
Luminosity 72.88[7] L
Temperature 7,980[7] K
Rotational velocity (v sin i) 123[7] km/s
Age 6.0×108[8] years
Other designations
Ruchbah, Ksora,[9] Rucba, Rucbar,[10] 37 Cassiopeiae, BD+59°248, FK5 48, HD 8538, HIP 6686, HR 403, SAO 22268[11]
Database references

Delta Cassiopeiae (δ Cassiopeiae, abbreviated Delta Cas, δ Cas), also named Ruchbah,[12] is an eclipsing binary star system in the northern circumpolar constellation of Cassiopeia.


δ Cassiopeiae (Latinised to Delta Cassiopeiae) is the star's Bayer designation.

It also bore the traditional names Ruchbah and Ksora; the former deriving from the Arabic word ركبة rukbah meaning "knee",[9] and the latter appeared in a 1951 publication, Atlas Coeli (Skalnate Pleso Atlas of the Heavens) by Czech astronomer Antonín Bečvář. Professor Paul Kunitzch has been unable to find any clues as to the origin of the name.[13] The star Alpha Sagittarii also bore the traditional name Ruchbah (as well as Rukbat). In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalogue and standardize proper names for stars. The WGSN approved the name Ruchbah for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names[12] (Alpha Sagittarii was given the name Rukbat).

In Chinese, 閣道 (Gé Dào), meaning Flying Corridor, refers to an asterism consisting of Delta Cassiopeiae, Iota Cassiopeiae, Epsilon Cassiopeiae, Theta Cassiopeiae, Nu Cassiopeiae and Omicron Cassiopeiae.[15] Consequently, Delta Cassiopeiae itself is known as 閣道三 (Gé Dào sān, English: the Third Star of Flying Corridor.)[16]


Delta Cassiopeiae is an eclipsing binary star system consisting of a pair of stars that orbit about each other over a period of 759 days.[4][17] The combined apparent visual magnitude of the two stars is 2.68, making it readily observable with the naked eye. However, this magnitude varies between +2.68 mag and +2.74 as the stars pass in front of each other.[18] Based on parallax measurements, this system is about 99.4 light-years (30.5 parsecs) from the Earth.[1]

The primary member of the system has a stellar classification of A5 IV, with the luminosity class of IV indicating that it has exhausted the hydrogen at its core and has begun to evolve through the subgiant phase into a giant star. It is calculated that it is 4% beyond the end of its main sequence lifetime,[7] with an age of about 600 million years.[8] It has expanded to about 3.9 times the Sun's radius.[8]

An excess infrared emission has been observed at a wavelength of 60 μm, which suggests the presence of a circumstellar debris disk. This emission can be characterized by heat radiated from dust at a temperature of 85 K, which corresponds to an orbital radius of 88 Astronomical Units, or 88 times the distance of the Earth from the Sun.[8] For comparison, the region of the remote Kuiper belt in the Solar System extends from 30–50 AU.


  1. ^ a b c d e f van Leeuwen, Floor (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752v1Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357  Note: see VizieR catalogue I/311.
  2. ^ a b c 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 
  3. ^ Gray, R. O.; Garrison, R. F. (1989). "The late A-type stars - Refined MK classification, confrontation with Stromgren photometry, and the effects of rotation". Astrophysical Journal Supplement Series. 70: 623. Bibcode:1989ApJS...70..623G. doi:10.1086/191349. 
  4. ^ a b 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 
  5. ^ Wilson, Ralph Elmer (1953), "General catalogue of stellar radial velocities", Washington, Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W 
  6. ^ Eggen, Olin J. (July 1998), "The Age Range of Hyades Stars", The Astronomical Journal, 116 (1): 284−292, Bibcode:1998AJ....116..284E, doi:10.1086/300413. 
  7. ^ a b c d e Zorec, J.; Royer, F. (2012). "Rotational velocities of A-type stars. IV. Evolution of rotational velocities". Astronomy & Astrophysics. 537: A120. arXiv:1201.2052Freely accessible. Bibcode:2012A&A...537A.120Z. doi:10.1051/0004-6361/201117691. 
  8. ^ a b c d e Rhee, Joseph H.; et al. (May 2007), "Characterization of Dusty Debris Disks: The IRAS and Hipparcos Catalogs", The Astrophysical Journal, 660 (2): 1556–1571, arXiv:astro-ph/0609555Freely accessible, Bibcode:2007ApJ...660.1556R, doi:10.1086/509912 
  9. ^ a b Bakich, Michael E. (1995), The Cambridge guide to the constellations, Cambridge University Press, p. 170, ISBN 0-521-44921-9 
  10. ^ Allen, Richard Hinckley (1899), Star-names and their meanings, G.E. Stechert, p. 148 
  11. ^ "V* del Cas -- Variable Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2010-02-21 
  12. ^ a b "IAU Catalog of Star Names". Retrieved 28 July 2016. 
  13. ^ Kunitzch, Paul; Smart, Tim (2006) [1986]. A Dictionary of Modern Star Names: A Short Guide to 254 Star Names and Their Derivations. Cambridge, Massachusetts: Sky Publishing Corporation. p. 62. ISBN 978-1-931559-44-7. 
  14. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016. 
  15. ^ (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.
  16. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived January 30, 2011, at the Wayback Machine., Hong Kong Space Museum. Accessed on line November 23, 2010.
  17. ^ Burnham, Robert (1978), Burnham's celestial handbook: an observer's guide to the Universe beyond the solar system, Dover books on astronomy and astrophysics, 1 (2 ed.), Courier Dover Publications, p. 492, ISBN 0-486-23567-X 
  18. ^ Kukarkin, B. V.; et al. (1971). "The third edition containing information on 20437 variable stars discovered and designated till 1968". General Catalogue of Variable Stars. General Catalogue of Variable Stars (3rd ed.). Bibcode:1971GCVS3.C......0K.