Doctor of Philosophy (PhD)
Physics and Astronomy
The Chandra Galactic Bulge Survey (GBS) is a shallow, wide field survey to search for and classify X-ray sources in the Galactic Bulge. Specifically, we are looking for Low Mass X-ray Binaries (LMXBs): systems containing either a neutron star or black hole that is accreting matter from a roughly stellar mass companion via Roche-Lobe overflow. My research uses optical, time-series photometry from the DECam instrument on the Blanco 4.0 m telescope at the Cerro Tololo Inter-American Observatory to identify counterparts to new X-ray sources in the GBS. For the systems that are variable in brightness in the optical, I use the morphology of the light curves and the relative proportion of optical and X-ray light, to identify high inclination systems through eclipses, and to determine what periodicity, if any, is present in the optical light. Combining these properties with optical spectroscopic campaigns, I can partially or fully classify the X-ray sources and their counterparts. The GBS contains a variety of X-ray sources, including Low Mass X-ray Binaries, Cataclysmic Variables, Intermediate Polars, Active Galactic Nuclei, W Ursa Majoris stars, RS Canum Venaticorum stars, active stars, flare stars, slowly pulsating B stars, and intermediate polars. Only a handful of sources are identified as potential new Low Mass X-ray Binaries in quiescence, which places limits on the number of such systems in the Galaxy. In addition to the GBS work, I have done work on Cataclysmic Variables, focusing on archival and historical light curves to get a glimpse at the evolution of these systems. In the case of classical novae, one popular evolutionary model suggests that post-eruption the system should fade in brightness over a timescale of 50-100 years between 0.2-1.0 mag/century. I make use of the Harvard College Observatory Plate Archives to search for photographic plates containing the target systems and manually extract magnitudes and dates to look for trends in the long term light curve.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Johnson, Christopher Bradley, "Variability of Optical Counterparts to X-ray Sources within the Galactic Bulge Survey" (2016). LSU Doctoral Dissertations. 2006.