Delta2 Lyrae

Delta2 Lyrae (δ2 Lyr) is a 4th magnitude star in the constellation Lyra, approximately 770 light years away from Earth. It is one of the M4II spectral standard stars.

Characteristics
It began life as a hot blue main sequence star, but now is a large cool asymptotic giant branch star with a degenerate carbon-oxygen 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 a star when still in the main sequence, but due to stellar mass loss it has lost 0.5 solar masses. Its photosphere has expanded to 290 times the size of the Sun, and is now radiating 12,500 times the luminosity of the Sun. Its photosphere has cooled to 3420 K, giving it a red hue typical of M-type stars.



It is the brightest member of the scattered open cluster Stephenson 1, also known as the δ Lyrae Cluster. Other known members include δ1 Lyrae, a handful of 8th-9th magnitudes stars, and at least thirty other stars down to 14th magnitude.

Variability
δ2 Lyrae is a variable star, probably a semiregular variable. It has a magnitude range of 4.22 to 4.33.

Companion stars
Multiple star catalogues list several companions to δ2 Lyrae, with designations such as ADS 11825. Two of them are a close pair of 10th magnitude stars about 87" from δ2, designated components B and C. The spectral type of the pair 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, the ADS 11825BC pair would be 24,000 AU away from δ2 Lyrae, and it would take 24,000 years for it to make an orbit. The two stars in the BC system take at least 10,500 years to make an orbit and are separated by 600 AU.

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.