Direct Detection of the L-Dwarf Donor in WZ Sagittae

Analysis of a large set of phase-resolved K-band spectra of the cataclysmic variable WZ Sge shows that the secondary star of this system appears to be an L-dwarf. Previous K-band spectra of WZ Sge found that the CO overtone bandheads were in emission. We show that absorption from the ¹²CO_(2,0) bandhead of the donor star creates a dip in the ¹²CO_(2,0) emission feature. Measuring the motion of this feature over the orbital period, we construct a radial velocity curve that gives a velocity amplitude of K_abs = 520 ± 35 km s^-1, consistent with the previously published values for this parameter.