Inverse Nova R Coronae Borealis
November 11, 2015
R Coronae Borealis is a low-mass, yellow supergiant star in the constellation Corona Borealis. It's the blinking star shown above. R Coronae Borealis is an example of a class of variable stars that fade by several magnitudes at irregular intervals. Over successive months it gradually returns to its normal peak brightness that gives it its alternative name of an Inverse Nova. It typically shines at a peak magnitude of around 6 (just visible to the unaided eye in a very dark sky) but fades to magnitude 14 or 15 at its minimum (see graph below photo).
I was aware that R Coronae Borealis had been sitting at its minimum for an overly long period of years when I imaged it in August 2013. So I was hoping that it would have started to brighten up a little again. Thus, I was very disappointed when I processed the data and had difficulty locating it since it was still at its minimum magnitude.
In May 2015, I was testing out a new imaging system and decided to observe in the Corona Borealis region. I really hadn't given any thought to R Coronae Borealis at the time, it was just that the constellation Corona Borealis was in a particularly good imaging position. On processing this data, I was amazed to see that after many years R Corona Borealis was now very much brighter, appearing to be around magnitude 7.5 in comparison with some nearby stars. The photo featured above blinks between the two images taken at near maximum and near minimum brightness for this impressive inverse nova.