Optical observations and cyclops post-shock region modelling of the polar V348 Pav

Abstract

Post-shock regions (PSR) of polar cataclysmic variables produce most of their luminosity and give rise to high circular polarization in optical wavelengths and strong variability on the white dwarf rotation period, which are distinctive features of these systems. To investigate the polar candidate V348 Pav, we obtained a comprehensive observational set including photometric, polarimetric, and spectroscopic data, which was used to constrain the post-shock properties of the system. The object presents high circular polarization ($\sim 30$ per cent) and high He II 4686A to H$\beta$ line ratio, confirming it is a polar. From both radial velocities and light curves, we determined an orbital period of 79.98~min, close to the orbital period minimum of CVs. The H$\beta$ radial velocity curve has a semi-amplitude of $141.4\pm 1.5$ km s${}^{-1}$. Doppler tomography showed that most of the spectral line emission in this system is originated in the region of the companion star facing the WD, possibly irradiated by the emission related to the PSR. We modelled the PSR using the Cyclops code. The PSR density and temperature profiles, obtained by a proper solution of the hydro-thermodynamic equations, were used in a 3D radiative transfer solution that takes into account the system geometry. We could reproduce the V348 Pav \textit{B, V, R}, and \textit{I} photometric and polarimetric data using a model with a WD magnetic field of $\sim 28$ MG, a WD mass of $\sim 0.85$~M${}_{\odot }$ and a low ($\sim 25^{\circ }$) orbital inclination. These values for the WD mass and orbital inclination are consistent with the measured radial velocities.

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