Keck Infrared Spectroscopy of WZ Sagittae: Detection of Molecular Emission from the Accretion Disk

Time-resolved IR spectroscopy of WZ Sge was obtained using NIRSPEC on Keck II. We detect CO and H₂ emission from the accretion disk, placing WZ Sge in a rarefied class of astronomical objects including young stellar objects and high-luminosity early-type stars. During the eclipse phase, the molecular emission greatly weakens, but no firm evidence for the secondary star is seen, allowing new limits on its luminosity to be determined. The detection of molecular emission provides physical properties T=3000 K and n_H>10¹⁰ cm^-3 within the outer disk. Such a cool, dense region not associated with areas of H I and He I emission provides the first observational confirmation of predictions made by accretion disk models.