Z Ursae Minoris (Z UMi) is a

carbon star A carbon star (C-type star) is typically an asymptotic giant branch star, a luminous red giant, whose Stellar atmosphere, atmosphere contains more carbon than oxygen. The two elements combine in the upper layers of the star, forming carbon monox ...

and

R Coronae Borealis variable An R Coronae Borealis variable (abbreviated RCB, R CrB) is an eruptive variable star that varies in luminosity in two modes, one low amplitude pulsation (a few tenths of a magnitude), and one irregular, unpredictably-sudden fading by 1 to 9 magni ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Ursa Minor Ursa Minor (, contrasting with Ursa Major), also known as the Little Bear, is a constellation located in the far northern celestial hemisphere, northern sky. As with the Great Bear, the tail of the Little Bear may also be seen as the handle of ...

. Z Ursae Minoris was discovered to be a

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

in 1934. It was catalogued as a probable

Mira variable Mira variables (named for the prototype star Mira) are a class of pulsating stars characterized by very red colours, pulsation periods longer than 100 days, and amplitudes greater than one magnitude in infrared and 2.5 magnitude at visual wave ...

, 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.

References

{{DEFAULTSORT:Z Ursae Minoris Ursa Minor R Coronae Borealis variables Ursae Minoris, Z Carbon stars