The Fe Line Flux Ratio as a diagnostic of the maximum temperature and the white dwarf mass of Cataclysmic Variables

Abstract

The flux ratio of Fe XXVI--Ly$\alpha$ to Fe XXV--He$\alpha$ lines ($I_{7.0}/I_{6.7}$) is a sensitive indicator of the maximum temperature ($T_{\max }$), and therefore the mass of white dwarf stars ($M_{\mathrm{WD}}$) in cataclysmic variables (CVs). To examine and calibrate the theoretical $I_{7.0}/I_{6.7}$--$T_{\max }$--$M_{\mathrm{WD}}$ relations, reliable measurements of $T_{\max }$ and $I_{7.0}/I_{6.7}$ are necessary. In this work, we conduct a thorough investigation on 3--50 keV X-ray spectra of 25 solar neighborhood magnetic and non-magnetic CVs based on archival \textit{NuSTAR} and \textit{Suzaku} observations. The measured $T_{\max }$ are compared to the $I_{7.0}/I_{6.7}$ and $M_{\mathrm{WD}}$. The results show the sampled CVs closely follow the theoretical $I_{7.0}/I_{6.7}$--$T_{\max }$ relation. Moreover, all the $M_{\mathrm{WD}}$ estimated from $I_{7.0}/I_{6.7}$ are consistent with the dynamically measured ones. We conclude that $I_{7.0}/I_{6.7}$ can be used as a good diagnostic for $T_{\max }$ and $M_{\mathrm{WD}}$ in both magnetic and non-magnetic CVs.

15 pages, 4 figures, Accepted for publication in ApJ