Mira variables, named after the prototype star Mira (Omicron Ceti) in the Cetus constellation, are pulsating stars characterized by a deep red hue. These red giants, in the twilight of their evolution, are on the brink of releasing their outer shells to form planetary nebulae, eventually transforming into white dwarfs. With pulsating periods longer than 100 days, their magnitude fluctuation at visual bands is around 2.5 magnitude.
The Mira-type star in R Aqr exhibits a variability period of just over a year, with its luminosity oscillating by a factor of 750. It boasts a mass estimated to be between 1 to 1.5 solar masses, whereas the white dwarf's mass ranges from 0.6 to 1 solar masses. These two celestial bodies are separated by roughly 11 astronomical units (AU - the average Earth-Sun distance).
The white dwarf attracts material from the Mira-type star, leading to the formation of a nebula known as Cederblad 211. This binary star system is located in a heavily dust-laden region, lending it a reddish appearance.
Images of R Aquarii have been captured using the Chandra X-ray Observatory's X-ray data (depicted in purple) and the Hubble Space Telescope's optical data (illustrated in red and blue).
Image Credit: X-ray: NASA/CXC/SAO/R. Montez et al.; Optical: Data: NASA/ESA/STScI, Processing: Judy Schmidt (CC BY-NC-SA)
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