A tomographic study of V691 CrA (X1822-371)

Abstract

We present Doppler and modulation tomography of the low-mass X-ray binary V691 CrA with data obtained using the 6.5-m Magellan Baade telescope at the Las Campanas Observatory in 2010 and 2011. The disc and hotspot are observed in H\alpha and He II (\lambda 4686) in both years. A clear image of the disc is seen in He II (\lambda 5411) using the 2010 data. We present the first tomography of the absorption line He I (\lambda 5876) and detect absorption near the L_1 point of the donor star. We also present the first modulation tomography of the emission line H\alpha and detect emission from the secondary. The H\alpha double peaks are imbedded in a deep absorption trough confirming the presence of Balmer line absorbing material in the system. Our observations of H\alpha show absorption in a larger phase range than in H\beta which could be due to heating up of sprayed matter from the hotspot as it travels downstream. We also suggest possible occultation of the H\alpha absorbing spray by the disc bulge at certain phases.