Epoch J2000.0 Equinox J2000.0
|Right ascension||18h 54m 30.2838s|
|Declination||+36° 53′ 55.007″|
|Apparent magnitude (V)||4.30v|
|Spectral type||M4 II|
|U−B color index||+1.65|
|B−V color index||+1.68|
|Radial velocity (Rv)||-25.55 km/s|
|Proper motion (μ)||RA: −7.36 mas/yr
Dec.: 4.06 mas/yr
|Parallax (π)||4.43 ± 0.18 mas|
|Distance||740 ± 30 ly
(226 ± 9 pc)
|Radius||286 - 381 R☉|
|Luminosity||12,900 - 23,100 L☉|
|Surface gravity (log g)||0 cgs|
|Temperature||3,550 - 3,650 K|
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 to the naked eye.
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.
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