The Fe Line Flux Ratio as a Diagnostic of the Maximum Temperature and the White Dwarf Mass of Cataclysmic Variables

Abstract

Abstract The flux ratio of Fe xxvi–Lyα to Fe xxv–Heα 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 WD) in cataclysmic variables (CVs). To examine and calibrate the theoretical I 7.0/I 6.7–T max–M WD relations, reliable measurements of T max and I 7.0/I 6.7 are necessary. In this work, we conduct a thorough investigation of 3–50 keV X-ray spectra of 25 solar neighborhood magnetic and nonmagnetic CVs based on archival NuSTAR and Suzaku observations. The measured T max are compared to the I 7.0/I 6.7 and M WD. The results show that the sampled CVs closely follow the theoretical I 7.0/I 6.7–T max relation. Moreover, all the M 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 WD in both magnetic and nonmagnetic CVs.