Study of the formation of circumbinary planets and comparison with SPHERE data

This thesis regards the research field concerning astrophysics of planet formation. In particular, it is focused on the study of the young (~20 Myr old) binary system V4046 Sgr and of the circumbinary disk surrounding it, discussing the evidence of the traces of eventual planets orbiting these stars. In fact, the aims of this work reside in both the analysis of certain disk's features and the study of the possibility for the formation of circumbinary planets in this system through the direct comparison with observational data from the SPHERE instrument, installed in the VLT in Chile. This work is structured as reported below, where its main features, objectives and results are outlined. Chapter 1 provides an overview of protoplanetary disks, in particular as concerns their structure and evolution, presenting the various mechanisms which led to the final structure of the disks we observe, and including both theoretical and observational argumentations. Instead, Chapter 2 considers the specific case of circumbinary disks, starting from the description of the interaction between the disk and the binary host and then reporting some concrete examples of studied circumbinary disks. Moreover, a Section is dedicated to circumbinary planets, as regards their features as well as their detection, especially through the direct imaging technique. After this abovementioned general introduction about the physics underlying this work, the description of the new-generation SPHERE instrument is reported in Chapter 3. In particular, besides introducing its main features, modules and capabilities, a Section is reserved for the various direct imaging techniques exploited by SPHERE, whereas the final part provides the latest SPHERE data concerning the discoveries of planets as well as protoplanetary disks, and the link between these scenarios. At this point, given this overview - needed for the comprehension of the topic of this work, it is possible to concentrate on the subject of this thesis, namely the binary system V4046 Sgr: its general description, including the main features of the binary as well as the disk surrounding it, is presented in Chapter 4. One of the peculiarities of the disk around V4046 Sgr is the radially-extended shadow it exhibits in the SPHERE images. Chapter 5 is then dedicated to the study of this shadow: invoking certain assumptions on the binary and on the profile of the disk in order to account for its presence, it has been possible to model the disk and compare the range of the radius of the shadow provided by the model with the observed value. The last part of this work is described in Chapter 6 and involves numerical simulations of the evolution of the dusty disk surrounding V4046 Sgr. In particular, an N-body program has been used in order to simulate the evolution of the dust particles in presence of planets, with the purpose to determine how many planets could reproduce the observational data, which show the evidence of two rings in the disk, and what their features are - taking into account the detectable limits of the instrument. Furthermore, a small Section presents the comparison between the observed dust-size distribution over the disk with the corresponding results from the simulations. Chapter 7 draws the conclusions of the thesis, listing the main achieved results as well as the limitations encountered, which could be overcome by future studies exploiting new instruments which are able to detect Saturnian-sized planets, since our simulations predict the presence of two Saturn/Neptune-sized planets orbiting between the two observed rings, and to provide more detailed dust emission data, in order to better constraint the observed shadow, the dust-size distribution and the other disk's features. Finally, Appendix A provides the main physical elements required in this work.