Pi Gruis

Pi Gruis (π Gruis) is a binary star system located in the constellation Grus (The Crane). It is approximately 530 light-years from Earth. The system is notable for containing a bright S-type star, π¹ Gruis, one of the largest and most luminous red giants known.

Properties

The primary component, π¹ Gruis (HD 208163), is a pulsating variable star classified as an S-type star. S-type stars are red giants that exhibit spectral lines of both s-process elements (such as strontium and barium) and molecules containing zirconium monoxide (ZrO), indicating the presence of these elements in the star's atmosphere. π¹ Gruis is a very evolved star, nearing the end of its life. It has expelled a large amount of its outer layers, forming a detached shell of dust and gas.

π² Gruis (HD 208162) is the fainter secondary component of the system, orbiting π¹ Gruis at a distance that is not precisely known.

Evolution

π¹ Gruis is in the late stages of stellar evolution. It has exhausted the hydrogen fuel in its core and is currently fusing helium into carbon and oxygen. The presence of s-process elements in its atmosphere indicates that it has undergone dredge-up events, where elements synthesized in the core are brought to the surface. Eventually, π¹ Gruis will eject its remaining outer layers as a planetary nebula, leaving behind a white dwarf remnant.

Observation

Pi Gruis is visible to the naked eye under dark skies, appearing as a reddish star. Its variability makes it a target of interest for amateur astronomers. The detached shell of dust and gas surrounding π¹ Gruis has been imaged by instruments such as the Very Large Telescope (VLT), revealing intricate spiral patterns within the expelled material.