QU Carinae: A SNeIa progenitor?

Abstract

Optical spectra obtained in 2006-2007 of the nova-like cataclysmic variable QU Car are studied for radial velocities (RVs), line profiles, and line identifications. We are not able to confirm the reported 10.9 h orbital period from 1982, partly because our sampling is not ideal for this purpose and also, we suspect, because our RVs are distorted by line profile changes due to an erratic wind. P-Cygni profiles are found in several of the emission lines, including those of C IV. Carbon lines are abundant in the spectra, suggesting a carbon enrichment in the donor star. The presence of [O III] 5007 Å and [N II] 6584 Å is likely due to a diffuse nebula in the vicinity of the system. The wind signatures in the spectra and the presence of nebular lines are in agreement with the accretion wind evolution scenario that has been suggested to lead to SNeIa. We argue that QU Car is a member of the V Sge subclass of cataclysmic variables, and a possible SNeIa progenitor. It is shown that the recent light curve of QU Car has ~1 mag low states, similar to the light curve of V Sge, strengthening the connection of QU Car with V Sge stars, supersoft X-ray sources, and SNeIa progenitors.