Svelare i misteri di AU Mic: misure delle velocità delle sue polveri circumstellari

In my MSc thesis project, I conducted an investigation into the edge-on debris disk surrounding the young (~ 23 Myr), nearby (~ 9.8 pc), M-type star AU Mic. The star has garnered significant interest recently following the SPHERE discovery of the presence of rapidly moving dust clumps that seem to originate from an unidentified source within the disk. The edge-on view of the disk means that only the sky-projected separations and velocities of the clumps have been measured through high-resolution SPHERE images. In the course of my MSc thesis work, I measured the velocity component along the line of sight - also known as radial velocity - of the dust clumps to provide a clearer understanding of their nature and dynamics, which continue to pose significant puzzling questions. In pursuit of this goal, I reduced and analysed high-resolution, near-infrared spectra of the clumps on the southeastern side of the debris disk surrounding AU Mic. The spectra were obtained using the CRIRES@VLT echelle spectrograph, which combines high spatial and spectral resolution. The analysis involves extracting the star and disk spectra, and defining the instrument's point spread function, which provides the flux distribution as a function of distance from the star. After identifying and removing the telluric lines, I defined a range of distances from the star to extract the spectrum of the starlight that is reflected by the dust present in the edge-on disk. I cross-correlated the dust-reflected starlight spectra with the spectrum of AU Mic and built a two-dimensional cross-correlation function, which provides the cross-correlation contrast as a function of radial velocity and distance from the star. I conducted the procedure multiple times across various spectral regions of the near-infrared spectra and co-added the two-dimensional cross-correlation functions to increase the signal-to-noise ratio. My work has resulted in a notable advancement in the methodology for extracting and analysing the CRIRES spectra. For the interpretation of the CRIRES radial velocities, I considered three different scenarios to describe the clumps around AU Mic: 1) circular ring of dust orbiting the star in a edge-on configuration; 2) outward expanding ring of dust orbiting the star in a edge-on configuration; and 3) orbiting and outward expanding circular ring of dust in an edge-on configuration. As a result of my analysis, I produce the separation-radial velocity image, that shows the spatial distribution of the dust as a function of radial velocity. It is a direct picture of the disk dynamics, but it does not allow me to draw any firm conclusion. Additional high spatial resolution images, along with a range of potential improvements that I identified and could be incorporated into the analysis of the data, are needed to determine the current position of the clumps and make conclusive claims.