Multi-wavelength studies of accretion and outflows in compact binaries

Abstract

The study of interacting compact binaries invokes a wide variety of astrophysical concepts, ranging from the physics of compact objects, accretion, stellar atmospheres and interiors, stellar and binary evolution. These systems host a stellar remnant, i.e. a white dwarf, neutron star or black hole – which produce a wide variety of exotic phenomena observable across the entire electromagnetic spectrum. Essentially all accreting systems exhibit evidence of mass-loss in the form of jets and disc winds, representing key mechanisms by which they interact with their environment. In this thesis, multi-wavelength (MW) observations encompassing different techniques and a wide range of timescales are used to investigate the accretion flow, outflows and evolution of two accreting compact binaries. In Chapter 2, the first comprehensive study on V341 Ara is presented, a 10th magnitude star recently identified as a cataclysmic variable star. The analysis of long-term and high resolution light curves allows the identification of both, the negative super-humps, and the super-orbital modulation of a tilted accretion disc that ultimately causes them. A recently developed disc instability model acting in a tilted disc is proposed as the underlying mechanism responsible of the eventual fading episodes observed in this source. The system’s mass ratio is obtained from time-resolved spectroscopy and the wind mass loss rate is constrained using spatially resolved [OIII] emission produced by a bow-shock. In Chapter 3, an overview of a major MW campaign is presented. One of the key ingredients of this campaign is the coordination of many of the major Earth- and space-based observatories from X-ray to radio, including near-infrared optical and ultraviolet time resolved spectroscopy and photometry of an extremely flaring low-mass X-ray binary. Chapter 4 is focused on the detection and implications of accretion disc winds in the ultraviolet spectrum we obtained during the campaign. In this research time-tagged far-ultraviolet spectroscopy is used to demonstrate that the absorption troughs are associated with a non-variable component of the spectrum, showing that flares and outflows are driven by different mechanisms; it also illustrates how wind signatures can be masked by flaring emission, even if the outflow is present all the time. This is crucial for the correct interpretation of all wind signatures. In Chapter 5, archival and new data is analysed to determine the properties of the companion star and line-of-sight absorption, to discuss the intrinsic luminosity and evolutionary stage of Swift J1858. All this is summarised in Chapter 6 along with future lines of research in these topics.

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