Structure of the pulsating red giant S Ori (artist's impression)

Sketch of the structure of a pulsating red giant, as derived by the recent interferometric study on S Orionis. The environment around the parent star is made up by three main components : a molecular shell (inner red layer), a dust shell (outer red layer) and a maser shell (red and green speckles). Grains of aluminum oxide constitute most of the dust shell (observed in the infrared band), while the maser radio emission comes from silicon monoxide molecules. The maser spots velocities indicates that the gas is expanding, at a speed of about 10 km/s.