An Empirical Correlation of $T_{\rm max}$ - $M_{\rm WD}$ of Dwarf Novae and The Average White Dwarf Mass in Cataclysmic Variables in the Galactic Bulge

TL;DR

This study establishes empirical correlations between X-ray spectral features and white dwarf mass in dwarf novae, enabling a more accurate estimate of the average WD mass in Galactic bulge cataclysmic variables, aligning with local measurements.

Contribution

It introduces semi-empirical correlations for non-magnetic CVs based on X-ray spectra, improving WD mass estimates in the Galactic bulge.

Findings

Average WD mass in Galactic bulge CVs is 0.81±0.07 M_sun.

Correlations enable WD mass estimation from X-ray spectral features.

Results align with optical measurements of local CVs.

Abstract

The mean white dwarf (WD) mass in the Galactic bulge cataclysmic variables (CVs) was measured by applying the the shock temperature-WD mass correlation of magnetic cataclysmic variables (mCVs) to the Galactic Bulge X-ray Emission (GBXE) spectra. However, the resulting mean WD mass is lower than that of the local CVs. This discrepancy could be explained by the dominating sources in the GBXE are non-mCVs instead of mCVs. In this work, we conduct an thorough investigation on the X-ray spectra of local DNe from \suzaku\ archives, and derive semi-empirical correlations between the shock temperature $T_{\rm max}$, the flux ratio of \fec\ to \feb\ lines, and WD mass for quiescent, non-magnetic CVs. By applying these correlations to the GBXE, we derive the average WD mass of CVs in the Galactic bulge to be $0.81\pm 0.07M_\odot$. This value is consistent with previous optical measurements of WD mass in local CVs.