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Delta2 Lyrae (δ2 Lyr) is a 4th magnitude star in the constellation Lyra, approximately 900 light years away from Earth. It is one of the M4II spectral standard stars, meaning it is a bright giant star with a surface temperature around 3,600 kelvins. It puts out more energy than 10,000 suns, although more than 90% of it at longer than visual wavelengths. Direct angular measurements, combined with the Hipparcos parallax, give a radius of 1.1〔 〕 - 1.3〔 〕 astronomical units, comparable to the size calculated from other observed data. It began life as a hot blue main sequence star, but now is a large cool asymptotic giant branch star with a degenerate helium core. It is a semi-regular variable star that has its brightness change by 0.2 magnitudes over an ill-defined period. Delta2 Lyrae was once thought to form a visual binary with the star Delta1 Lyrae, but it does not, only appearing to do so if seen from earth's direction. The spectral type of the nearby star system CCDM J18545+3654BC suggests that they are at the same distance as Delta2 Lyrae, which could mean that the three stars form a triple star system. In this case, CCDM J18545+3654BC would be 24,000 AU away from Delta2 Lyrae, and it would take 24,000 years for it to make an orbit. The two stars in the CCDM J18545+3654BC system take at least 10,500 years to make an orbit and are separated by 600AU. Delta2 Lyrae is the brightest member of the scattered open cluster Stephenson 1. ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Delta2 Lyrae」の詳細全文を読む スポンサード リンク
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