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Beta Ophiuchi
Beta Ophiuchi (β Oph, β Ophiuchi) is a star in the equatorial constellation of Ophiuchus. It has the traditional names Celbalrai,〔 which comes from the Arabic كلب الراعي ''kalb al-rā‘ī'' meaning "shepherd dog". It is also called Cheleb,〔 Kelb Alrai, or sometimes just Alrai. The apparent visual magnitude of this star is 2.7,〔 which is readily visible to the naked eye even from urban skies. The distance to this star can be estimated using parallax measurements, yielding a value of .〔
This is a giant star with a stellar classification of K2 III.〔 Although it is only 13% greater in mass than the Sun,〔 it has reached a stage in its evolution where the atmosphere has expanded to about 12 times the Sun's radius and is radiating 63 times the luminosity of the Sun.〔 Its outer envelope is relatively cool with an effective temperature of 4,467 K,〔 giving it the orange hue typical of K-type stars.〔 Like some other K-type giants, β Ophiuchi has been found to vary very slightly (0.02 magnitudes) in brightness.〔,〔
Cebalrai is a member of the thin disk population. It is following a low eccentricity orbit through the Milky Way galaxy that carries it between a distance of from the Galactic Center and up to above or below the galactic plane.〔
== Planetary system?==
Radial velocity variations with a period of 142 days hint about the possible presence of a planetary companion orbiting Beta Ophiuchi. Thus far, no planetary object has been confirmed; while periodic radial pulsations caused by intrinsic stellar variability could explain the observed variations.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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