Gaia 19cwm -- an eclipsing dwarf nova of WZ Sge type with a magnetic white dwarf

TL;DR

Gaia 19cwm is a WZ Sge type cataclysmic variable with a magnetic white dwarf, exhibiting eclipses, stable short-period variability, and low X-ray luminosity, indicating it is an intermediate polar with accretion disk features.

Contribution

This study provides detailed spectral, photometric, and modeling analysis of Gaia 19cwm, identifying it as a magnetic white dwarf in a WZ Sge system and classifying it as a low-luminosity intermediate polar.

Findings

Orbital period of 86.32 minutes with eclipses observed.

Stable 6.45-minute period attributed to white dwarf rotation.

White dwarf mass estimated at 0.66 solar masses.

Abstract

The spectral and photometric studies of the cataclysmic variable Gaia 19cwm (or ZTF19aamkwxk) have been performed. Based on the analysis of long-term variability, it is concluded that the object belongs to WZ Sge type stars. The light curves show eclipses recurring with an orbital period of $86.32048 \pm 0.00005$ min, as well as an out-of-eclipse variability with a period of $\approx 6.45$ min. The latter period is stable for $\sim 4$ years and appears to correspond to the rotation of a magnetic white dwarf, i.e., Gaia 19cwm is an intermediate polar. The Gaia 19cwm spectra show photospheric lines of the white dwarf, and Doppler tomograms demonstrate the presence of an accretion disk and a hot spot. Analysis of the eclipse light curve gives an estimates of the white dwarf mass $M_1 = 0.66\pm0.06$ M$_{\odot}$, the donor mass $M_2 = 0.073 \pm 0.015$ M$_{\odot}$, and the orbital inclination $i=83.8 \pm 1.1^{\circ}$. Modeling of the spectral energy distribution gives the white dwarf temperature of $T_{eff}\approx 13000 $ K. The X-ray luminosity $L_X = (1.6 \pm 0.3) \times 10^{31}$ erg/s allows to assign Gaia 19cwm to a small group of low-luminosity intermediate polars.