J194827-131733: a new eclipsing magnetic cataclysmic variable

Abstract

Cataclysmic Variables (CVs) are binary star systems composed of a main sequence star that donates material to a white dwarf companion, which acts as the accretor, typically within an accretion disk. However, when the white dwarf possesses strong magnetic fields, the formation of a disk is prevented, resulting in systems known as polars. Here, I present the discovery of a polar CV in this study. As part of the observational program of CVs using ESO Xshooter, I observed the system J194827-131733. During a 3.5-hour observation period, 81 spectra were captured, which I applied telluric correction with Molecfit in the VIS arm. This large dataset is combined with the long term high cadence TESS photometry, I perform a deep analysis on this system. The Lomb- Scargle periodogram of the TESS light curve revealed a principal orbital period of 5.197 ± 0.015 hours, with other significant peaks being harmonics of the principal. The system displays distinct characteristics indicative of being an eclipsing polar CV: (1) Notable He II emission lines in its spectrum, likely originating near the white dwarf rather than from the irradiated hemisphere of the donor stars, (2) the absence of double-peaked emission lines, suggesting the lack of an accretion disk, and (3) single periodicity. The creation of trailed spectra suggests a configuration where the donor star is heavily irradiated by the white dwarf, and accretion likely follows a ballistic stream. There is speculation that the accretion curtain lies along the line of sight. Additionally, unlike many polars where He II emission emanates from the irradiated face, in this system, the emission is predominantly produced near the white dwarf, similar to the asynchronous polar BY Cam. The discovery of this polar system, previously uncatalogued, unveils unusual parameters, including one of the longest orbital period, and significantly higher luminosity compared to known polar CVs. Therefore, this is an interesting system for multi-wavelength follow up studies.