VLTI's view on the circumstellar environment of cool evolved stars

Infrared spectro-interferometry provides us with a unique opportunity to study the circumstellar environment of cool evolved stars in great detail, with spectral and spatial information disentangled. Recently, ESO's Very Large Telescope Interferometer (VLTI) has shed new light on the molecule and dust formation close to the photosphere or the structure of circumstellar disks around cool evolved stars. Our VLTI/MIDI observations of the oxygen-rich Mira star RR Sco have revealed the wavelength dependence of the angular size of the Mira star from 8 to 13 μm, which can be well explained by the presence of extended and dense H₂O layers and an optically thin dust shell. On the other hand, our MIDI observations of the silicate carbon star IRAS08002-3803 indicate the presence of an optically thick circumbinary disk, but the dust chemistry in the disk has turned out to be more complicated than previously thought. These results demonstrate the power of spectro-interferometry for obtaining new insights into the circumstellar environment of cool evolved stars.