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Yellow giant star in the constellation Corona Borealis From Wikipedia, the free encyclopedia
Delta Coronae Borealis, Latinized from δ Coronae Borealis, is a variable star in the constellation Corona Borealis. Its apparent magnitude varies regularly between apparent magnitude 4.57 and 4.69, and it is around 170 light-years distant.
A visual band light curve for Delta Coronae Borealis, plotted from data published by Fernie (1991).[1] The 59 day rotation period is shown in red. | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Corona Borealis |
| Right ascension | 15h 49m 35.64682s[2] |
| Declination | +26° 04′ 06.2065″ἴ[2] |
| Apparent magnitude (V) | 4.57 - 4.69[3] |
| Characteristics | |
| Spectral type | G5III-IV Fe-1[4] |
| U−B color index | +0.32[5] |
| B−V color index | +0.78[5] |
| Variable type | RS CVn?[3] |
| Astrometry | |
| Radial velocity (Rv) | −20.356±0.035[6] km/s |
| Proper motion (μ) | RA: -78.83[2] mas/yr Dec.: -65.28[2] mas/yr |
| Parallax (π) | 19.7137 ± 0.1820 mas[7] |
| Distance | 165 ± 2 ly (50.7 ± 0.5 pc) |
| Absolute magnitude (MV) | +1.18[8] |
| Details | |
| Mass | 2.4[9] M☉ |
| Radius | 7.4[9] R☉ |
| Luminosity | 34.3[9] L☉ |
| Surface gravity (log g) | 3.29[8] cgs |
| Temperature | 5,180[9] K |
| Metallicity [Fe/H] | −0.12[8] dex |
| Rotation | 59[9] days |
| Rotational velocity (v sin i) | 4.56[8] km/s |
| Age | 851[8] Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
δ Coronae Borealis is a yellow giant star of spectral type G3.5III that is around 2.4 times as massive as the Sun and has swollen to 7.4 times its radius. It has a surface temperature of 5180 K.[11] For most of its existence, Delta Coronae Borealis was a blue-white main sequence star of spectral type B before it ran out of hydrogen fuel in its core. Its luminosity and spectrum suggest it has just crossed the Hertzsprung gap, having finished burning core hydrogen and just begun burning hydrogen in its shell. It is a strong source of X-rays due to its hot corona.[12]
In 1989, it was noticed that the brightness of δ Coronae Borealis is not constant. Approximately every 45 days, its brightness changes sinusoidally between 4.57 and 4.69, too small to be noticed without close monitoring. The evolutionary state of the star and its probably rotation period mean that the variations may be due to its rotation with different parts of the surface having spots or different temperatures. This would make it an RS Canum Venaticorum variable.[13] The period has since been refined to 59 days and this is now accepted as the star's rotation period.[9]
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