Infrared contamination in Galactic X-ray novae

The most widely used means of measuring the mass of black holes in Galactic binaries - specifically the X-ray novae - involves both radial velocity measurements of the secondary star, and photometric measurements of its ellipsoidal variability. The latter is important in constraining the inclination and mass ratio, and requires as direct a measure of the flux of the secondary as possible. Up to now, such measurements have been preferentially carried out in the near-infrared (NIR: 1-2.5 μm), where the flux from the cooler secondary is expected to dominate over that from the accretion disc. However, here we present evidence of a significant non-stellar contribution to the NIR flux in many of those quiescent X-ray novae that are thought to contain a black hole primary. We discuss origins of this excess and the effect of such contamination on Galactic black hole mass measurements.