The Detection of13CO and Other Apparent Abundance Anomalies in the Secondary Stars of Long-Period Cataclysmic Variables

We present moderate resolution (R > 1,800) infrared K-band spectra of twelvelong-period (Porb > 6 hr) cataclysmic variables. We detect absorption linesfrom the photospheres of the secondary stars in every system, even though twoof the m were undergoing outubrsts. We have attempted to assign spectral typesto each of the secondary stars, and these classifications are generallyconsistent with previous determinations/estimates. We find evidence forabundance anomalies that include enhancements and/or deficits for all of thespecies commonly found in the K-band spectra of G- and K-type dwarfs. There is,however, only one common abundance anomaly: extremely weak CO features. Onlytwo of the twelve objects appeared to have normal levels of CO absorption. Weinterpret this as evidence for low carbon abundances. In addition, we detect13CO absorption in four of the twelve objects. Depleted levels of 12C andenhanced levels of 13C indicate that material that has been processed in theCNO cycle is finding its way into the photospheres of CV secondary stars. Insystems with luminous accretion disks, we find that the spectrum of thesecondary star is contaminated by a source that flattens (reddens) thecontinuum. While free-free or classical accretion disk spectra are flatter thanthe blackbody-like spectra of G and K dwarfs, removal of such contaminationfrom the K-band data results in spectra in which the absorption features becometoo strong to be consistent with those of G and K dwarfs.Comment: 43 pages, 20 figure