R Coronae Borealis

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R CrB

R Coronae Borealis
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Corona Borealis
Right ascension 15h 48m 34.4149s
Declination +28° 09′ 24.296″
Apparent magnitude (V) 5.9m
Characteristics
Spectral type G0Iab:pe
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
Astrometry
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
Distance 6,200[1] ly
(1,900[1] pc)
Absolute magnitude (MV) −5.85[1]
Details
Mass ~0.8 M
Luminosity ~19,000[1] L
Surface gravity (log g) 0.15[1] cgs
Temperature 6,900[1] K
Other designations
V* R CrB, GSC2 N1330022410, 2MASS J15483440+2809242, AG+28° 1513, GSC 02039-01605, N30 3552, TD1 18592, BD+28° 2477, HD 141527, PLX 3581, TYC 2039-1605-1, EM* CDS 886, PPM 104338, GC 21257, HIP 77442, RAFGL 4219, YZ 28 7350, GCRV 9116, HR 5880, ROT 2225, AAVSO 1544+28A, IRAS 15465+2818, SAO 84015.
Database references
SIMBAD data

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".

AAVSO light curve showing R Coronae Borealis' behavior over approximately 8 years. The dates given are Julian day numbers.

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.

History[edit]

Variability of R CrB has been discovered by the English astronomer, Edward Pigott in 1795.[2][3] It was known as Variabilis Coronae,[4] "Variable of Corona". In 1935 it was the first star shown to have a different chemical composition than the sun via spectral analysis.[5][6]

References[edit]

  1. ^ a b c d e f Bibcode1975A&A....44..383S
  2. ^ Frommert, H., Kronberg, Ch., R Coronae Borealis: SEDS
  3. ^ Davis, K., (2000) R Coronae Borealis: AAVSO
  4. ^ Allen, R. H., (1963) Star Names: Their Lore and Meaning, (rep.) Dover Publications, Inc., p. 178. [1]
  5. ^ Hockey, Thomas (2009). The Biographical Encyclopedia of Astronomers. Springer Publishing. ISBN 978-0-387-31022-0. Retrieved August 22, 2012. 
  6. ^ 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. 

External links[edit]