R Coronae Borealis
R Coronae Borealis
Epoch J2000.0 Equinox J2000.0
|Right ascension||15h 48m 34.4149s|
|Declination||+28° 09′ 24.296″|
|Apparent magnitude (V)||5.9m|
|B−V color index||0.56|
|V−R color index||0.0|
|J−H color index||0.275|
|J−K color index||0.8|
|Variable type||R CrB|
|Radial velocity (Rv)||24.8 km/s|
|Proper motion (μ)||RA: -2.10 mas/yr
Dec.: -11.52 mas/yr
|Parallax (π)||0.54 ± 0.72 mas|
|Absolute magnitude (MV)||−5.85|
|Surface gravity (log g)||0.15 cgs|
R Coronae Borealis is a yellow supergiant star, and is the prototype of the RCB class of variable stars, which fade by several magnitudes at irregular intervals. R Coronae Borealis itself normally shines at approximately magnitude 6, just about visible to the naked eye, in the constellation of Corona Borealis, but at intervals of several months to many years fades to as faint as magnitude 14. Over successive months it gradually returns to its normal brightness, giving it the nickname "Fade-Out star," or "Reverse Nova".
The cause of this behaviour is believed to be a regular build-up of carbon dust in the star's atmosphere. The sudden drop in brightness may be caused by a rapid condensation of dust, resulting in much of the star's light being blocked. The gradual restoration to normal brightness results from the dust being dispersed by radiation pressure.
Even basic data for this star is not known with any accuracy. It is too distant for accurate direct measurement and models of the class are poorly defined.
Variability of R CrB has been discovered by the English astronomer, Edward Pigott in 1795. It was known as Variabilis Coronae, "Variable of Corona". In 1935 it was the first star shown to have a different chemical composition than the sun via spectral analysis.
- Bibcode: 1975A&A....44..383S
- Frommert, H., Kronberg, Ch., R Coronae Borealis: SEDS
- Davis, K., (2000) R Coronae Borealis: AAVSO
- Allen, R. H., (1963) Star Names: Their Lore and Meaning, (rep.) Dover Publications, Inc., p. 178. 
- Hockey, Thomas (2009). The Biographical Encyclopedia of Astronomers. Springer Publishing. ISBN 978-0-387-31022-0. Retrieved August 22, 2012.
- Berman, Louis (1935). "The Spectrum Analysis of the Hot Carbon Star, R Coronae Boreali". The Astrophysical Journal 81: 369. Bibcode:1935ApJ....81..369B. doi:10.1086/143644. Retrieved August 22, 2012.
- Variable Star of the Month January, 2000: R Coronae Borealis
- Entry in the Encyclopedia of Astrobiology, Astronomy, and Spaceflight
- ESO 34/07 - Science Release: "Star Caught Smoking"