Optical and infrared emission from discs, jets and nebulae associated with X-ray binaries

Abstract

X-ray binaries are binary star systems in which a compact object (a neutron star or a black hole) and a relatively normal star orbit a common centre of mass. Since the discovery of X-ray binaries with the first X-ray telescopes in the 1960s, astronomers have tried to understand how these bizarre objects behave, and why. Some change in X-ray luminosity by 10^8 orders of magnitude on timescales of days to months due to an increased transfer of mass from the star towards the compact object. Many X-ray binaries are detected at all observable frequencies, from radio to gamma-rays. It has been found that many different sources of emission, which peak at different frequencies, are present in X-ray binary spectra and together they produce the observed broadband spectrum. However, disentangling these components has proved challenging. Much of the work in this thesis concerns disentangling the components that occupy the optical and near-infrared (NIR) region of the spectrum of X-ray binaries; possibly the region in which the relative contributions of the different components are least certain. In particular one component, the synchrotron emission from jets of outflowing matter, is found in this work to contribute ubiquitously to the optical and NIR light of X-ray binaries with relatively faint stars. These results confirm that the jets are powerful and in some of this work, observations of the jets interacting with the surrounding matter are used to infer their power.