Infrared spectroscopy of cataclysmic variables - III. Dwarf novae below the period gap and nova-like variables

We present K-band spectra of the short-period dwarf novae YZ Cnc, LY Hya, B K Lyn, T Leo, SW UMa and WZ Sge, the nova-like variables DW UMa, V1315 Aql, RW Tri, VY Scl, UU Aqr and GP Com, and a series of field dwarf stars with spectral types ranging from K2 to M6. The spectra of the dwarf novae are dominated by emission lines of H I and H e I. The large velocity and equivalent widths of these lines, in conjunctio n with the fact that the lines are double-peaked in the highest inclination systems, indicate an accretion disc origin. In the case of YZ Cnc and T Le o. for which we obtained time-resolved data covering a complete orbital cyc le, the emission lines show modulations in their equivalent widths that are most probably associated with the bright spot (the region where the gas st ream collides with the accretion disc). There are no clear detections of th e secondary star in any of the dwarf novae below the period gap, yielding u pper limits of 10-30 per cent for the contribution of the secondary star to the observed K-band flux. in conjunction with the K-band magnitudes of the dwarf novae, we use the derived secondary star contributions to calculate lower limits to the distances to these systems. The spectra of the nova-like variables are dominated by broad, single-peake d emission lines of H I and He I - even the eclipsing systems we observed d o not show the double peaked profiles predicted by standard accretion disc theory. With the exception of RW Tri, which exhibits Na I, Ca I and (CO)-C- 12 absorption features consistent with a M0V secondary contributing 65 per cent of the observed K-band flux, we find no evidence for the secondary sta r in any of the nova-like variables. The implications of this result are di scussed.