Exploring the long-term variability and evolutionary stage of the interacting binary DQ Velorum

Abstract

To progress in the comprehension of the double periodic variable (DPV) phenomenon, we analyse a series of optical spectra of the DPV system DQ Velorum during much of its long-term cycle. In addition, we investigate the evolutionary history of DQ Vel using theoretical evolutionary models to obtain the best representation for the current observed stellar and orbital parameters of the binary. We investigate the evolution of DQ Vel through theoretical evolutionary models to estimate the age and the mass transfer rate which are compared with those of its twin V393 Scorpii. Donor subtracted spectra covering around 60% of the long-term cycle, allow us to investigate time-modulated spectral variations of the gainer star plus the disc. We compare the observed stellar parameters of the system with a grid of theoretical evolutionary tracks computed under a conservative and a non-conservative evolution regime. We have found that the EW of Balmer and helium lines in the donor subtracted spectra are modulated with the long-term cycle. We observe a strenghtening in the EWs in all analysed spectral features at the minimum of the long-term cycle which might be related to an extra line emission during the maximum of the long-term variability. Difference spectra obtained at the secondary eclipse support this scenario. We have found that a non-conservative evolutionary model is a better representation for the current observed properties of the system. The best evolutionary model suggests that DQ Vel has an age of 7.40 x 10^{7} yr and is currently in a low mass transfer rate (-9.8x10^{-9} Msun/yr) stage, after a mass transfer burst episode. Comparing the evolutionary stages of DQ Vel and V393 Sco we observed that the former is an older system with a lower mass transfer rate. This might explain the differences observed in the physical parameters of their accretion discs.