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

摘要

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 Keckspectrum of VY Aqr suggests an M0 spectral type, much hotter than previously derived. We re-reduce theoriginal data for VY Aqr that were obtained using ISAAC on the Very Large Telescope (VLT) and find abest-fitting spectral type of M6 for VY Aqr. We are unable to reconcile the two data sets. We analyze newphase-resolved optical spectroscopy of VY Aqr, obtained using UVES on the VLT, to derive the mass ra-tio, and show that the mass of its secondary star is very likely below the stellar/substellar boundary. We alsopresent and model phase-resolved JHK infrared light curves for both objects, and g- and I-band light curvesfor EI Psc. While the light curve models for EI Psc are consistent with its spectral type, we are unable tomodel the light curves of VY Aqr without assuming binary star parameters outside the published range for thisobject.