Sigmavariables

Sigmavariables, also known as sigma variables, are a class of variable stars that exhibit variations in their light output due to the pulsations of their outer layers. These stars are named after the Greek letter sigma (σ), which is used to denote their variability. Sigmavariables are typically red giants or supergiants, which means they are in the late stages of stellar evolution.

The light variations in sigmavariables are typically semi-regular, meaning they do not follow a strict periodic pattern. This semi-regular variability is thought to be caused by the interaction between the star's pulsations and its outer convection zone. The pulsations can cause the star's radius to change, leading to variations in its brightness.

Sigmavariables are relatively rare compared to other types of variable stars. They are typically found in the late stages of stellar evolution, and their variability is often a result of their large size and complex internal structures. Despite their rarity, sigmavariables are an important class of stars for astronomers studying stellar evolution and variability.

Some well-known examples of sigmavariables include R Hydrae and VY Canis Majoris. R Hydrae is a red supergiant that exhibits semi-regular variability, while VY Canis Majoris is a red hypergiant that is one of the largest known stars. Both of these stars are important objects for studying the late stages of stellar evolution and the physics of variable stars.