[Thesis]. Manchester, UK: The University of Manchester; 2013.
From the main sequence onwards, stars of intermediate masses (1-8 Solar masses) eject
a large portion of their mass with rates as high as 0.0001 Solar masses per year during
their transition through the Asymptotical Giant Branch (AGB) stage. The outflows are
shaped by the same mechanisms that shape the ejecta, which in turn appear to depart
from spherical symmetry as early as the AGB stage. The ejecta are then evolving into
asymmetrical structures. Stars like that are giant factories of dust, responsible
for the enrichment of their surrounding Galactic medium in metals heavier than helium.
Depending on their abundances during the AGB stage, the stars are either oxygen-rich
or carbon-rich, and as such, the dust produced in their atmospheres is either O-rich
or C-rich. The chemical composition of the ejecta, indicates the stellar chemistry
at the moment of ejection. The disruption of the spherical symmetry of the mass loss
can be caused by fast rotation, stellar magnetic fields or binarity, the latter being
the most efficient and favourable mechanism. Such mechanisms can lead to the creation
of circumstellar, equatorial, dusty structures, like discs, torii or spirals. Due
to their small relative sizes, compared to their surrounding nebulae, they can be
studied at best with the use of infrared interferometric techniques. We report the
discovery of three such structures in sources at three different evolutionary stages,
respectively, with the use of single- and multi-aperture interferometry. In the C-rich
AGB star V Hya we imaged via aperture masking in the near-infrared, a complex and
possibly orbiting structure, which is embedded within the star's molecular torus.
Our MIDI observations in the mid-infrared have revealed, a silicate disc within the
symbiotic nebula M2-9 that is currently being shaped by the central binary system
within its core, and a C-rich disc-like structure in the born-again star Sakurai's
Object, that is also aligned to an asymmetry found in its surrounding planetary nebula.
Finally, we compare the properties of the structures found here with those found in
the literature in order to establish a relation between late stellar evolution and
the existence of dusty structures.