INFRARED PHOTOMETRY AND SPECTROSCOPY OF VY Aqr AND EI Psc: TWO SHORT-PERIOD CATACLYSMIC VARIABLES WITH CURIOUS SECONDARY STARS

Abstract

We present new K-band spectra of VY Aqr and EI Psc obtained with NIRSPEC on the Keck II telescope. We find a best-fitting spectral type of K4 for EI Psc, in agreement with the previous classification. The Keck spectrum of VY Aqr suggests an M0 spectral type, much hotter than previously derived. We re-reduce the original data for VY Aqr that were obtained using ISAAC on the Very Large Telescope (VLT) and find a best-fitting spectral type of M6 for VY Aqr. We are unable to reconcile the two data sets. We analyze new phase-resolved optical spectroscopy of VY Aqr, obtained using UVES on the VLT, to derive the mass ratio, and show that the mass of its secondary star is very likely below the stellar/substellar boundary. We also present and model phase-resolved JHK infrared light curves for both objects, and g- and I-band light curves for EI Psc. While the light curve models for EI Psc are consistent with its spectral type, we are unable to model the light curves of VY Aqr without assuming binary star parameters outside the published range for this object.