Young X-Ray Binary Populations: Metallicity Effects and a Diagnostic for Electron-Capture Supernovae Senior Honors Thesis Department of Physics and Astronomy Northwestern University

High mass X-Ray binaries (HMXBs) are two body systems that consist of a nuclear burning star accreting matter onto a compact object (CO) such as a neutron star (NS) or black hole (BH). Stellar material from the donor heats up as it falls into the deep potential well of the accretor, emitting blackbody radiation with a characteristic X-Ray spectrum. There are two separate processes through which HMXBs can produce X-Rays. In wind accretion systems, plasma in the stellar winds of the donor star is propelled isotropically, with some falling directly onto the compact object. In Roche Lobe Overflow (RLO) HMXBs, the two stars begin to orbit so closely, that the first Lagrange point for the two body system falls inside the radius of the donor. Mass outside the equipotential surface will be transfered onto the compact object, resulting in the accretion of large quantities of matter. There are many inputs which determine the likelihood of a given binary system developing into a HMXB. Most importantly, the primary (initially more massive) star must be large enough to form a NS or BH. The orbital separation and eccentricity of the binary must be set such that the donor is close enough to transfer substantial quantities of matter onto the accretor, but not so closely that the two stars merge early in their lifetimes. Usually, stars in a binary system evolve almost independently of each other, following a stellar track depending on the initial mass and chemical composition of the star. However, if the binary system experiences a common envelope (CE) phase (where the outer layers of the two stars merge), mass can be transfered between stars, altering their subsequent single star evolution tracks. Matter falling into a CO loses a tremendous amount of potential energy which must be lost in the form of black body radiation. Thus, HMXBs are extremely bright, almost always with a luminosity of at least 10 32 erg s −1 and sometimes emitting radiation at the Eddington limit. The lifetime of HMXBs is highly variable, bound first by the longevity 2 of the donor star after the supernova event of the accretor. HMXBs may also appear bright only during certain stages of the donors stellar evolution, increasing the variability of HMXB sources over time. While some small RLO systems can maintain stable X-Ray luminosities for hundreds of Myr, the total number of bright sources is strongly dependent on …