The Structures of X-ray Binary Systems V801 Ara and Cyg X-3 from Doppler Tomography

We present spectroscopic observations of two X-ray binary systems, V801 Ara and Cyg X-3. We observed V801 Ara in the optical in 2014 with IMACS on the Magellan/Baade telescope at Las Campanas Observatory and Cyg X-3 in the near-infrared in 2015 with GNIRS on the Gemini North telescope. Both spectra contain strong emission features that are suitable for tomography, allowing us to map the systems in velocity space. Our tomograms show continuous emission of H_alpha and H_beta from V801 Ara’s accretion disk. The center of the accretion disk does not coincide with the neutron star’s estimated center of mass (estimated using K1 = 102 km s-1 and K2 = 360 km s-1 from Casares et al. 2006, MNRAS, 373, 1235), possibly indicating eccentricity in the disk. The tomograms also do not show a hot spot where the accretion stream hits the disk, implying a low accretion rate. Due to insufficient orbital phase coverage in our GNIRS observations, we are unable to produce significant tomograms of Cyg X-3.