Delta² Lyrae
| Observation data Epoch J2000.0 Equinox J2000.0 |
|
|---|---|
| Constellation | Lyra |
| Right ascension | 18h 54m 30.2838s |
| Declination | +36° 53′ 55.007″ |
| Apparent magnitude (V) | 4.30 |
| Characteristics | |
| Spectral type | M4 II |
| U−B color index | +1.65 |
| B−V color index | +1.67 |
| Astrometry | |
| Radial velocity (Rv) | -26.4 km/s |
| Proper motion (μ) | RA: -6.73 mas/yr Dec.: 3.26 mas/yr |
| Parallax (π) | 3.63 ± 0.56 mas |
| Distance | approx. 900 ly (approx. 280 pc) |
| Details | |
| Mass | 7.3[2] M☉ |
| Radius | 275 R☉ |
| Luminosity | 6,500 L☉ |
| Temperature | 3,637[2] K |
| Other designations | |
Delta2 Lyrae (δ2 Lyr) is a 4th magnitude star in the constellation Lyra, approximately 900 light years away from Earth. It is a class M4II star, meaning it is a bright giant star with a surface temperature under 3,500 kelvins. It shines with the light of 6,500 Suns, and has a radius of 200 solar radii, or 0.95 times the radius of Earth's orbit, though other measurements give an even larger radius of 1.3 astronomical units.[3]
It began life 75 million years ago as a bluish white B3 spectral type star of six solar masses, with a surface temperature between 11,000 and 25,000 kelvins. It now possesses a dead helium core, and is becoming an even larger giant. 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.[3]
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 trinary 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.[3]
[edit] References
- ^ "Simbad Query Result", Simbad, http://simbad.u-strasbg.fr/simbad/sim-id?protocol=html&Ident=*+12+Lyr, retrieved October 15, 2007
- ^ a b Tsuji, Takashi (May 2007), "Isotopic abundances of Carbon and Oxygen in Oxygen-rich giant stars", in Kupka, F.; Roxburgh, I.; Chan, K., Convection in Astrophysics, Proceedings of IAU Symposium #239 held 21-25 August, 2006 in Prague, Czech Republic, pp. 307–310, Bibcode 2007IAUS..239..307T, doi:10.1017/S1743921307000622
- ^ a b c Kaler, James B., "Delta-2 Lyrae", Stars (University of Illinois), http://www.astro.uiuc.edu/~kaler/sow/delta2lyr.html, retrieved October 15, 2007
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