R Coronae Borealis
Z Ursae Minoris was discovered to be a variable star in 1934. It was catalogued as a probable Mira variable, due to its red colour and variations over several hundred days. It was discovered to be a carbon star in a survey published in 1985, and subsequently found also to be hydrogen-deficient. After fading by almost six magnitudes in 1992, it was classified as an R Coronae Borealis variable. It was confirmed as an R Coronae Borealis variable, one of the coolest in the class, after its spectrum was analysed in 2006.