Epoch J2000 Equinox J2000
|Right ascension||01h 25m 48.95147s|
|Declination||+60° 14′ 07.0225″|
|Apparent magnitude (V)||2.68|
|U−B color index||+0.13|
|B−V color index||+0.13|
|Variable type||Eclipsing binary|
|Radial velocity (Rv)||−6.7 km/s|
|Proper motion (μ)||RA: 296.57 mas/yr
Dec.: –49.22 mas/yr
|Parallax (π)||32.81 ± 0.14 mas|
|Distance||99.4 ± 0.4 ly
(30.5 ± 0.1 pc)
|Rotational velocity (v sin i)||123 km/s|
Delta Cassiopeiae (δ Cas, δ Cassiopeiae) is a star in the northern circumpolar constellation of Cassiopeia. It has the traditional names Ksora and Ruchbah, derived from the Arabic word ركبة rukbah meaning "knee". It is not to be confused with Alpha Sagittarii, which also is called Ruchbah or Rukbat.
In Chinese, 閣道 (Gé Dào), meaning Flying Corridor, refers to an asterism consisting of δ Cassiopeiae, ι Cassiopeiae, ε Cassiopeiae, θ Cassiopeiae, ν Cassiopeiae and ο Cassiopeiae. Consequently, δ Cassiopeiae itself is known as 閣道三 (Gé Dào sān, English: the Third Star of Flying Corridor.)
The Proper Name Ksora for Delta Cassiopeiae 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.
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. 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. Based on parallax measurements, this system is about 99.4 light-years (30.5 parsecs) from the Earth.
The primary member of the system has a stellar classification of A5III-IVv, 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 has expanded to about 3.9 times the Sun's radius. The lower case 'v' in the stellar class indicates that the spectrum shows signs of variation. The system has an estimated age of 600 million years.
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. For comparison, the region of the remote Kuiper belt in the Solar System extends from 30–50 AU.
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