RCB Light Curve

Background

R Coronae Borealis is the prototype of RCB variable stars. It was discovered in 1797 by Edward Pigott and Henry C Engfield (Pigott & Englefield, 1797) and ever since has been seen to undergo irregular sharp dips in flux followed by a gradual recovery (Clayton, 1996). The cause of the decrease in flux of RCB variables is thought to be due to build up of carbon dust in the stellar atmosphere at irregular intervals which obscures the photosphere, in the case of R Coronae Borealis the sharp dips in flux can be as great as 8 magnitudes and occur over a time period of a few weeks (Clayton, 1996).

Light Curve

I started my observations on 29/01/17 and intend to carry on observing the star over the coming months to record any rise or decrease in flux.

Magnitude has been estimated using the astrometry feature in IRIS image processing software (Buil, 2014) which returns a visual magnitude as well as an objects position on the celestial sphere by comparing the flux ratio between the selected target and the surrounding stars it detects in the image. From using the traditional method of comparing the brightness of stars by eye to estimate the brightness of a star I estimated R CRB to be m7.9 from my first observation (29/01/2017) however observations of other amateur astronomers show a visual magnitude of m8.0 - m8.1 (AAVSO, 2017) around the same period which agrees with the magnitude calculated by using IRIS of m8.1.

References

AAVSO, 2017. American Association of Variable Star Observers. [Online]
Available at: https://www.aavso.org/lcg
[Accessed 29 January 2017].

Clayton, G. C., 1996. The R Coronae Borealis Stars. Publications of the Astronomical Society of the Pacific, Volume 108, pp. 225-241.

Christian Buil, 2014 . IRIS. [Online] 

Available at: http://www.astrosurf.com/buil/us/iris/iris.htm

[Accessed 29 January 2017].

Pigott, E., Englefield, H. C., 1797. On the periodical changes of brightness of two fixed stars. Philosophical Transactions, Volume 87, pp 133-141.