Optical and X-ray studies of HEAO-1 X-ray sources

Abstract

Identifications of optical counterparts of the weaker, hard (>2 keV) HEAO-1 X-ray sources continue to be made. In this thesis results are presented of some of this work, with particular emphasis on the follow-up studies of the Galactic sources. An overview of the identification process, including the justification, aims, and methodology is given. A brief historical discussion of other X-ray surveys puts the HEAO-1 mission in perspective; it is the most recent deepest flux limited, unbiased all-sky survey in the 2-10 keV region. The importance of this survey in both the study of newly identified sources, and a wider statistical analysis of the various classes of optical counterpart is highlighted. To date there are -500 optical identifications covering all classes, from nearby stellar sources to extragalactic objects, and the projected number of identifications is expected to exceed -600 by the time the final catalog of counterparts is completed in 1990. Whereas this thesis is primarily concerned with the Galactic sources, the most populous single source of optical counterparts are the active galactic nuclei. A short presentation is given of some initial results in this area. Results of identifications of bright star counterparts, which include both the Be X-ray binary and RS Canum Venaticorum classes, are presented. For the latter it is shown that the usually variable, hard X-ray emission is likely to be a result of enhanced Solar-like flaring activity. The bulk of the work presented in this thesis is the identification and studies of X-ray emitting cataclysmic variables. Detailed optical, and some X-ray observations are presented of three such systems. One of these 1H0542-407, is shown to be a DQ Herculis (or intermediate polar) magnetic variable, with a wealth of optical and X-ray periodicities. These can be explained in terms of the orbital sidebands, with the dominant optical period arising from X-ray reprocessing on the secondary star or accretion disk bulge. Reflection of the harder X-rays (>2 keV) also occurs in this region. Radial velocity variations are seen at both the orbital and spin periods, the latter interpreted as magnetospheric disruption of the inner regions of the accretion disk. Similar velocity variations, on a longer timescale, are also seen in H0534-581, which is also proposed to be a DQ Her system, although the X-ray pulsations are much weaker. Finally the serendipitouslv discovered nova-like cataclysmic variable, LB 1800, which is identified with the transient X-ray source 4U0608-49, is discussed. This binary is a reasonably bright (V-13.5) deep eclipsing (AV-3) system with a relatively long orbital period (-5.6 h). Both the emission line and continuum eclipses have similar morphology, and in particular widths, indicating the radial extent of both emitting regions is equal.