• accretion disks
• astrophysics
• disk-winds
• microquasars
• polarimetry
• spectroscopy

This thesis presents an observational study of SS433, the prototype of the microquasars. The microquasars are highly energetic compact sources emitting from the X-rays to the radio domain. They are the compact analogues of Quasars and Active Galactic Nuclei (AGN) and display a variety of physical processes also found also in the AGN: non thermal radiative processes, such as synchrotron emission, time dependent variability, flares, accretion disks that power the central engine (the black hole) and polarization variability. They are characterized by extended, relativistic jets extending up to ~ 10^(17-20) cm. SS433 is a binary system composed of a compact object (it is not well established if it is a neutron star or a black hole) orbiting with an A4-7 supergiant (Ib). The compact object (“the gainer”) is accreting mass from the A supergiant (the “loser”) and surrounded by an accretion disk. A part of which is ejected through extended, mildly relativistic (beta = 0:26) jets, directed along the axial directions of the disk. The binary has an orbital period of 13:08 days and, furthermore, the disk and the jets precess with a period of 162 days.
The thesis project studies the inner regions of the SS433 system, its binary nature, its accretion disk structure and its dynamical processes and extended flows. The system is investigated using optical spectroscopic, polarimetric and photometric new and archival observations. The aim of this work is to derive and constrain the properties of the accretion process and the radiative, circumstellar environment of the binary. Polarimetry is not frequently used in astrophysics but it is an unique and important diagnostic tool that provides otherwise inaccessible information related to the geometrical properties of a system (e. g., due by scattering) or to the presence of magnetic fields (e. g., synchrotron radiation is polarized).
Spectroscopy, based on line profiles and intensities yields the dynamical information of the environment.
Spectra and phometry, have been newly acquired with the Liverpool Telescope (LT), located at La Palma. Other spectra were obtained from the ESO public archives to extend the temporal baseline and phase coverage, for both precessional and orbital phases. The polarimetric data was newly acquired with the LT using the RINGO3 polarimeter and from a twin telescope located on the Hawaii, where a more precise polarimeter (Dipol-2) is installed. The calibration and data reduction involving polarimetry and photometry was performed by the candidate (except for Dipol-2), while the LT spectra were reduced by a standard LT pipeline for consistency but checked separately. The ESO archival spectra were already pipeline calibrated. During the LT observations, a flaring event was detected and for the first time for SS433 polarization data covered this event. The main part of the work is the study of the spectra, in particular a multiline comparison of the spectral phase dependent variations to understand the accretion process and the dynamical characteristics of the system, using radiative hydrodynamic arguments. For the polarimetry, a method has been developed to remove the Interstellar Medium (ISM) contribution to the polarization, and the first intrinsic polarization measurements of SS433 have been obtained. The final derived picture sheds light on a complex environment, which consists of a non Keplerian, thick accretion disk and a complex wind coming from the central, accreting source.
The thesis is organized as follows. The first chapter presents SS433, i. e., its properties, physical characteristics and the type of work and diagnostic methods used in the thesis. The second chapter is a theoretical overview of those radiative transfer and optical polarization processes that are useful to understand the subsequent analysis and the derived results. The third chapter describes the instrumentation, reduction and calibration methods developed by the candidate (and the LT staff) and applied to the data. The fourth chapter describes the ISM removal procedure and the analysis and description of the lines profiles and their variation with precessional and orbital phases. The fifth and last chapter presents the results and discussion of the thesis, together with the analysis of the flaring event.