Infrared Spectroscopic Observations of the Secondary Stars of Short
  Period Sub-Gap Cataclysmic Variables
  We present K-band spectroscopy of short period, "sub-gap" cataclysmic
variable (CV) systems obtained using ISAAC on the VLT. We show the infrared
spectra (IR) for nine systems below the 2-3 hour period gap: V2051 Oph, V436
Cen, EX Hya, VW Hyi, Z Cha, WX Hyi, V893 Sco, RZ Leo, and TY PsA. We are able
to clearly detect the secondary star in all but WX Hyi, V893 Sco, and TY PsA.
We present the first direct detection of the secondary stars of V2051 Oph, V436
Cen, and determine new spectral classifications for EX Hya, VW Hyi, Z Cha, and
RZ Leo. We find that the CO band strengths of all but Z Cha appear normal for
their spectral types, in contrast to their longer period cousins above the
period gap. This brings the total number of CVs and pre-CVs with moderate
resolution (R >~ 1500) IR spectroscopy to sixty-one systems: nineteen pre-CVs,
thirty-one non-magnetic systems, and eleven magnetic or partially magnetic
systems. We discuss the trends seen in the IR abundance patterns thus far, and
highlight a potential link between anomalous abundances seen in the IR with the
C IV/N V anomaly seen in the ultraviolet. We present a compilation of all
systems with sufficient resolution IR observations to assess the CO band
strengths, and, by proxy, obtain an estimate on the C abundance on the
secondary star.
