POLARIMETRÍA INTERFEROMÉTRICA MEDIANTE EL USO DE TRAZAS DE CLAUSURA

In modern astronomical radio interferometry, one of the greatest difficulties to be solved in order to analyse the data obtained in the observations is the correction of the instrumental effects that contaminate the visibility matrices. These matrices are built by decomposing the incident radiation in each pair of antennas of the interferometer into two orthogonal polarization components, which allows us to calculate the correlation products between said antennas. Traditionally, the closure amplitude and closure phase have proven to be key for radiointerferometry thanks to their invariance to gain effects in the antennas, although their use is quite limited, as they are not invariant to calibration, since they are sensitive to instrumental polarization effects. However, in 2020, Avery E. Broderick and Dominic W. Pesce proposed the closure traces (see Broderick&Pesce 2020), a new type of interferometric observable invariant to any instrumental effect that is expressible by means of Jones matrices. The application of the closure traces to observations of astronomical interferometry could allow us to obtain information on the state of polarization of the observed sources that is robust and independent of the instrumental polarization. However, the closure quantities do not save all the information related to the structure of the source, since these quantities suffer from various degenerations.

In this thesis, a detailed study of the properties of closure traces and their connection with traditional closure quantities is proposed, deepening into the behaviour of traces in the case of a double source. Next, we analyse the behaviour of the closure traces on a set of simulated interferometric data to check their robustness against instrumental effects and, simultaneously, study the degenerations under changes in the Poincare sphere. Finally, we calculate the closure traces for real data taken with the Atacama Large mm/submm Array (ALMA) telescope and the results of the analysis are compared with those obtained from standard image reconstruction techniques. Consequently, at the end of the thesis, we will have a more complete understanding of the closure traces and the potential of this new interferometric observable in the analysis of interferometric polarimetry observations.