Program: GN-2011A-Q-13

Low mass X-ray binaries (LMXBs) are interacting systems in which a neutron star or black hole accretes material from a donor star via an accretion disk. LMXBs provide excellent environments for studying the evolution of compact objects, disk accretion dynamics, and physics in the strong gravity regime, but this work is hampered by the limited information on key parameters such as the masses of the compact accretors. Since 2004, we have obtained NIR spectra of several LMXBs for which we have precisely determined compact object masses along with abundance anomalies to constrain models of black hole formation and evolution. We propose to extend our studies to fainter targets by obtaining NIR spectra of the LMXB XTE J1118+480 with Gemini-N. XTE J1118+480 is the centerpiece of numerous studies of accretion and general relativity, but its black hole mass has not yet been accurately determined. Using NIR spectra from Gemini and contemporaneous light curves from APO, we will determine the black hole mass in XTE J1118+480 and model the donor star spectrum to place limits on the evolutionary history of the system.