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.[10]
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.[9] Delta2 Lyrae was a 5.0
M☉ star when still in the
main sequence, but due to
stellar mass loss it has lost 0.5 solar masses.[5] Its
photosphere has expanded to 290 times the size of the Sun,[6] and is now radiating 12,500 times the
luminosity of the Sun. Its photosphere has cooled to 3,420
K (3,150 °C),[5] giving it a red hue typical of
M-type stars.[11]
Lyra with the
δ Lyrae pair and surrounding cluster stars left of centre
It is the brightest member of the scattered
open clusterStephenson 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.[12][4]
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.[14] 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.[citation needed]
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.[9]
^
abcdSamus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1.
Bibcode:
2009yCat....102025S.
^
abEggen, O. J. (April 1968). "Photometric evidence for the existence of a delta Lyrae cluster". Astrophysical Journal. 152: 77.
Bibcode:
1968ApJ...152...77E.
doi:
10.1086/149525.
^Levesque, E. M.; Massey, P.; Olsen, K. A. G.; Plez, B.; Josselin, E.; Maeder, A.; Meynet, G. (2005). "The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not as Cool as We Thought". The Astrophysical Journal. 628 (2): 973–985.
arXiv:astro-ph/0504337.
Bibcode:
2005ApJ...628..973L.
doi:
10.1086/430901.
S2CID15109583.