R Coronae Borealis

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Star
R Coronae Borealis
AladinLite
Observation
dates equinox :  J2000.0 , epoch : J2000.0
Constellation Northern crown
Right ascension 15 h 48 m 34.42 s
declination + 28 ° 09 ′ 24.3 ″
Apparent brightness 5.89 (5.71-15.2) mag
Typing
B − V color index +0.77 
U − B color index +0.29 
R − I index +0.18 
Spectral class C0.0 (F8pep)
Variable star type RCB 
Astrometry
Radial velocity (27.8 ± 0.8) km / s
parallax (0.76 ± 0.06)  mas
distance (4,300)  ly
(130)  pc
Proper movement 
Rec. Share: (−2.45 ± 0.14)  mas / a
Dec. portion: (−11.81 ± 0.34)  mas / a
Physical Properties
Other names
and catalog entries
Bonn survey BD + 28 ° 2477
Bright Star Catalog HR 5880 [1]
Henry Draper Catalog HD 141527 [2]
Hipparcos catalog HIP 77442 [3]
SAO catalog SAO 84015 [4]
Tycho catalog TYC 2039-1605-1 [5]
2MASS catalog 2MASS J15483440 + 2809242 [6]

R Coronae Borealis ( R CrB for short ) is an eruptive variable star in the northern crown constellation . R Coronae Borealis is a 6th magnitude star, the brightness of which drops sharply at irregular intervals.

R Coronae Borealis is a hydrogen- poor red supergiant with a carbon- rich atmosphere . The drops in brightness are likely due to ejected soot clouds obscuring the star's photosphere . R Coronae Borealis is the prototype for the class of eruptive variable R Coronae Borealis stars named after him .

According to data from the Gaia spacecraft , the star is just over 4000 light years away ( Gaia DR2 ).

Fluctuations in brightness

Light curve of R Coronae Borealis from 1990 to 2017

The English astronomer Edward Pigott discovered in 1795 that R Coronae Borealis has strong fluctuations in brightness. In its “normal state”, the star has only slight fluctuations of around a tenth of a magnitude. However, every few years or decades the brightness drops massively from its normal value. Then the star will be significantly darker for a few months or years. How much and for how long it darkens is different every time. There is no pattern and no fixed minimum. Then it either returns to its normal brightness or the next darkening overlaps the previous one.

The possible cause is believed to be that carbon dust accumulates in the stellar atmosphere . This dust is expelled and condenses into soot clouds some distance from the star. These block the light from the star. The blockage disappears after a while as the soot is dispersed by radiation pressure .

In August 2007, R Coronae Borealis began its strongest blackout to date. In 33 days, its luminosity fell to the 14th magnitude. This was followed by a slower further darkening up to the 15th magnitude in June 2009. Then it slowly became brighter again and reached the 12th magnitude towards the end of 2011. This was an unusually deep and long minimum. Even after that, the star did not return to its normal brightness, but experienced further strong fluctuations in the following years.

literature

Web links

Individual evidence

  1. ↑ a b c d e R CrB. In: SIMBAD . Center de Données astronomiques de Strasbourg , accessed on October 31, 2018 .
  2. ^ Hipparcos catalog (ESA 1997)
  3. ↑ a b c R CrB. In: VSX. AAVSO, accessed October 31, 2018 .
  4. ↑ a b Bright Star Catalog
  5. ^ H. Saio: Radial and Nonradial Pulsations in RCB and EHe-B Stars . In: Hydrogen-Deficient Stars ASP Conference Series . 391, 2008, p. 69. bibcode : 2008ASPC..391 ... 69S .
  6. ^ CL Watson: The International Variable Star Index (VSX) . In: The Society for Astronomical Sciences 25th Annual Symposium on Telescope Science. Held May 23-25 . 25, 2006, p. 47. bibcode : 2006SASS ... 25 ... 47W .
  7. ^ A b Steve B. Howell, Travis A. Rector, Donald Walter: Optical Spectroscopy at Deep Light Minimum of R Coronae Borealis . In: Publications of the Astronomical Society of the Pacific . 125, No. 930, 2013, pp. 879-888. bibcode : 2013PASP..125..879H . doi : 10.1086 / 672163 .