MATISSE imaging of carbon-rich stars - towards understanding the complex AGB mass-loss picture

The asymptotic giant branch (AGB) is the final stage in the evolution of low-to-intermediate mass stars. Subject to strong convective dredge-up and slow mass ejection, AGB stars are split into three main categories depending on which chemical element (carbon, oxygen or fairly equal) is most abundant in the atmosphere. With mass-loss being the reason behind the ending of the AGB stage, this phase in stellar evolution is very important for the enrichment of the interstellar medium with heavy elements. Planetary nebulae (PNe) are believed to form from the ejected atmospheres of AGB stars, via the interaction of a companion with the circumstellar environment in those cases where asymmetries are present. However, the ratio of asymmetric PNe to AGB stars that have a companion are not matching very well, a fact which places questions on the currently accepted spherically symmetric mass-loss model of single AGB stars. Carbon-rich envelopes seem to be more asymmetric when compared to oxygen-rich ones in the near-infrared wavelength regime, another aspect that needs further analysis. With the help of VLTI/MATISSE one can gather more information regarding the observed asymmetries in AGB stellar envelopes and PNe, by observing the dust and gas at the same time and probing the dust forming region. This will help provide some insight into the wind formation mechanism for single and binary stars. As part of an ESO Large Programme a few AGB stars, covering the different chemical types and binarity status, are observed with MATISSE. This presentation will cover the carbon-rich part of the sample and will go into the results of the image reconstruction analysis of the MATISSE observations, as well as any potential implications for the issues we are currently faced with regarding AGB mass-loss.