Catching VY Sculptoris in a low state

TL;DR

This study analyzes the binary system VY Scl during its low state using spectroscopy and photometry, revealing system parameters and stellar component motions with minimal accretion disc influence.

Contribution

First detailed spectroscopic and photometric analysis of VY Scl in a low state, providing constraints on binary parameters and stellar masses.

Findings

Orbital period of 3.84 hours identified.

Mass ratio M2/M1 constrained to 0.43.

White dwarf mass estimated at 0.6 Msol.

Abstract

Context. In the context of a large campaign to determine the system parameters of high mass transfer cataclysmic variables, we found VY Scl in a low state in 2008. Aims. Making use of this low state, we study the stellar components of the binary with little influence of the normally dominating accretion disc. Methods. Time-resolved spectroscopy and photometry of VY Scl taken during the low state are presented. We analysed the light-curve and radial velocity curve and use time-resolved spectroscopy to calculate Doppler maps of the dominant emission lines. Results. The spectra show narrow emission lines of Halpha, Hbeta, HeI, NaID, and FeII, as well as faint TiO absorption bands that trace the motion of the irradiated secondary star, and Halpha and HeI emission line wings that trace the motion of the white dwarf. From these radial velocities, we find an orbital period of 3.84 h, and put constraints on binary parameters such as the mass ratio M2/M1 of 0.43 and the inclination of 15 deg. With a secondary's mass between 0.3 and 0.35 Msol, we derive the mass for the white dwarf as M1 = 0.6-0.1 Msol.