V1082-Sgr: A magnetic cataclysmic variable with a lobe-filling companion star

Abstract

V1082 Sgr is a cataclysmic variable with accretion luminosity above 10 34 erg s −1 , indicating a mass transfer rate above 10 −9 M ⊙ yr −1 . However, its K type companion was suggested to be under-filling its Roche lobe (RL), making the high mass transfer rate a mystery. In this work we propose a possible model to explain this discrepancy. The system is proposed to be an intermediate polar, with its K type companion filling its RL. The mass of the white dwarf star is evaluated to be 0.77 ± 0.11M ⊙ from both X-ray continuum fitting and Fe line flux ratio measurements. We make numerical simulations to search for the possible progenitors of the system. The results show that a binary with an initial 1.5-2.5M ⊙ companion in a 1-2 day orbit (or an initial 1.0-1.4M ⊙ companion in a 3.2-4.1 day orbit) may naturally evolve to a cataclysmic variable with a ∼ 0.55 ± 0.11M ⊙ , Roche-lobe filling companion in a 0.86 day orbit. The effective temperature of the donor star, the mass transfer rate, and the derived V band magnitude are all consistent with previous observations.