Structure of a Mira star: S Ori under scrutiny

Using the VLTI and the VLBA facilities, an international team of astronomers has made a detailed study of the environment of S Orionis, a Mira-type pulsating red giant star.

They have made coordinated observations of three separate layers within the star’s outer envelope: the molecular shell, the dust shell, and the maser shell. S Ori shows significant phase-dependences of photospheric radii and dust shell parameters. Al₂O₃ dust grains and SiO maser spots form at relatively small radii of ∼1.8−2.4 photospheric radii.

Their results suggest an increased mass loss and dust formation close to the surface near the minimum visual phase, and a more expanded dust shell after visual maximum.