Catching VY Sculptoris in a low state^⋆,⋆⋆

¹ European Southern Observatory, Casilla 19001, Santiago 19, Chile
e-mail lschmidt@eso.org
² INAF-OATS, Via G.B. Tiepolo 11, 34143 Trieste, Italy
³ NASA Ames Research Center, PO Box 1, M/S 244-30, Moffett Field, CA 94035, USA
⁴ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁵ Department of Physics, University of Warwick, Coventry CV4 7AL, UK
⁶ Cerro Tololo Inter-American Observatory, Casilla 603, La Serena, Chile
⁷ Department of Physics and Astronomy, SUNY Stony Brook, Stony Brook, NY 11794-3800, USA

Received: 31 December 2017
Accepted: 25 April 2018

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 lightcurve 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 Hα, Hβ, He I, Na I D, and Fe II, as well as faint TiO absorption bands that trace the motion of the irradiated secondary star, and Hα and He I 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°. With a secondary’s mass between 0.3 and 0.35 M_⊙, we derive the mass for the white dwarf as M₁ = 0.6–1.1 M_⊙.