An x-ray and optical study of AM Herculis Systems
thesisposted on 15.12.2014, 10:40 by Keith Brendan. Sohl
An observational study of AM Herculis system is presented, incorporating photometry and spectroscopy at both X-ray and optical wavelengths. Much of this thesis focuses upon one system, HU Aqr, a bright eclipsing system discovered by ROSAT. HU Aqr is unique amongst AM Hers because it has eclipses and possesses an accretion stream with significant optical flux, thus allowing detailed study of the nature of the accretion flow for the first time.;Strong constraints on the accretion stream in HU Aqr have been obtained from optical photometry and spectroscopy. Changes to the mass accretion rate lead not only to variations in the mean flux from the system, but also to changes in the number of accreting poles and to alterations to the accretion geometry. A correlation analysis of the short timescale flickering in the data reveals a strong association between the photometry and polarimetry during the absorption dip. This is interpreted as arising from density structure within the accretion stream. The spectroscopic data reveals a highly complex emission pattern arising within the stream. A model has been developed which is used to measure the brightness distribution along the stream using both eclipse and emission line data. This has demonstrated that the line and continuum emission regions are located in well-defined yet separate regions within the stream.;Further evidence for complex density structure in the accretion stream has been obtained from short timescale variations in the X-ray flux during the absorption dip of both HU Aqr and UZ For. In Hu Aqr, the first detection has been made of coronal emission from the secondary star in an AM Her system. Both systems have also provided clear evidence for spectral structure within the accretion region, comprising a hard core of emission with a softer region surrounding it.;This X-ray analysis was extended to include a total of 30 systems in a study of the soft X-ray light curves and phase-resolved spectral behaviour of AM Her systems. In addition to confirming that the overall morphology of AM Her light curves is broadly consistent with most of our expectations, evidence for structured accretion regions, similar to those found in HU Aqr and UZ For, were discovered in six other AM Her systems.