Bow shocks, nova shells, disc winds and tilted discs: The nova-like V341 Ara has it all

Abstract

V341 Ara was recently recognized as one of the closest (d~ 150 pc) and brightest (V~10) nova-like cataclysmic variables. This unique system is surrounded by a bright emission nebula, likely to be the remnant of a recent nova eruption. Embedded within this nebula is a prominent bow shock, where the system´s accretion disc wind runs into its own nova shell. In order to establish its fundamental properties, we present the first comprehensive multiwavelength study of the system. Long-term photometry reveals quasi-periodic, super-orbital variations with a characteristic time-scale of 10-16 d and typical amplitude of ~1 mag. High-cadence photometry from theTransiting Exoplanet Survey Satellite (TESS) reveals for the first time both the orbital period and a ´negative superhump´ period. The latter is usually interpreted as the signature of a tilted accretion disc. We propose a recently developed disc instability model as a plausible explanation for the photometric behaviour. In our spectroscopic data, we clearly detect antiphased absorption and emission-line components. Their radial velocities suggest a high mass ratio, which in turn implies an unusually low white-dwarf mass. We also constrain the wind mass-loss rate of the system from the spatially resolved [O iii] emission produced in the bow shock; this can be used to test and calibrate accretion disc wind models. We suggest a possible association between V341 Ara and a ´guest star´ mentioned in Chinese historical records in AD 1240. If this marks the date of the system´s nova eruption, V341 Ara would be the oldest recovered nova of its class and an excellent laboratory for testing nova theory.