K-band interferometric imaging of the M-type Mira star ‘R Car’

The final stage of low to intermediate-mass stars, also known as the asymptotic giant branch (AGB), presents circumstellar envelopes (CSE); however the mechanisms that lead to the formation of these structures, at least in M-type AGBs, are still not well understood. In order to grasp the characteristics of the CSE, it has been found that the CO molecule plays an important role due to its stability against dissociation, making it a tracer of the gas density over a wide radial range.

In the present work, we explore K-band interferometric data of the M-type (M5/8) Mira star R Car obtained in 2018 with the Very Large Telescope Interferometer (VLTI) of ESO's Paranal Observatory, using the instrument GRAVITY. The analysis includes: (i) a parametric fit to the interferometric data, and (ii) an image reconstruction of the continuum and of the CO band heads. The results so far show asymmetric and extended structures that might be related to outflows; whether these outflows are originated in the inner or outer parts of the star is still under discussion. The previous results are important in the understanding of the formation of CSE in M-type AGB stars.