S Orionis

S Orionis is a Mira variable star located in the constellation Orion. It is a red giant star nearing the end of its life, characterized by significant pulsations in its brightness over a period of roughly 420 days.

As a Mira variable, S Orionis undergoes dramatic changes in luminosity and spectral type. During its brightest phases, it can reach a magnitude of around 7, making it visible with binoculars. At its faintest, it dims to magnitude 14, requiring a telescope to observe. These variations are caused by radial pulsations within the star's atmosphere, which expand and cool, then contract and heat, leading to changes in surface temperature and consequently, brightness.

S Orionis is surrounded by a circumstellar envelope (CSE) of gas and dust expelled from the star during its pulsation cycles. This CSE is particularly prominent in infrared wavelengths and contains molecules such as silicon monoxide (SiO) and water (H2O). The study of this CSE provides insights into the mass loss processes that occur in evolved stars like S Orionis, enriching the interstellar medium with heavy elements.

The distance to S Orionis is estimated to be approximately 1,440 light-years. Understanding the precise distance is crucial for accurately determining the star's intrinsic luminosity and the physical properties of its circumstellar envelope.

Observations of S Orionis across the electromagnetic spectrum, from radio waves to optical and infrared light, continue to provide valuable information about the late stages of stellar evolution and the process of mass return to the galaxy.