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

TL;DR

This paper investigates V1082 Sgr, a magnetic cataclysmic variable with a Roche-lobe filling companion star, proposing a model to explain its high mass transfer rate and analyzing its evolutionary history through numerical simulations.

Contribution

The study introduces a model where the companion star fills its Roche lobe in an intermediate polar system, resolving the discrepancy between observed luminosity and companion star filling status.

Findings

White dwarf mass estimated at 0.77±0.11 M_sun.

Progenitor systems likely involved initial companions of 1.0-2.5 M_sun.

Simulated evolution matches observed donor star properties.

Abstract

V1082 Sgr is a cataclysmic variable with accretion luminosity above $10^{34}$erg s$^{-1}$, indicating a mass transfer rate above $10^{-9}M_{\odot}$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 $0.77\pm0.11M_{\odot}$ 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--2.5$M_{\odot}$ companion in a 1--2 day orbit (or an initial 1.0--1.4$M_{\odot}$ companion in a 3.2--4.1 day orbit) may naturally evolve to a cataclysmic variable with a $\sim 0.55 \pm 0.11M_{\odot}$, 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.