New Spectroscopy of U Gem

Abstract

We present new optical spectroscopic observations of U Geminorum obtained during a quiescent stage. We perform a radial velocity analysis of three Balmer emission lines yielding inconsistent results. Assuming that the radial velocity semi amplitude accurately reflects the motion of the white dwarf, we arrive at masses for the primary which are in the range of Mwd = 1.21−1.37M☉. Based on the internal radial velocity inconsistencies and results produced from the Doppler tomography - wherein we do not detect emission from the hot spot, but rather an intense asymmetric emission overlaying the disc, reminiscent of spiral arms - we discuss the possibility that the overestimation of the masses may be due to variations of gas opacities and a partial truncation of the disc.