Measuring the masses of Intermediate Polars with NuSTAR: V709 Cas, NY Lup and V1223 Sgr

Abstract

The X-ray spectra of intermediate polars can be modelled to give a direct measurement of white dwarf mass. Here, we fit accretion column models to NuSTAR spectra of three intermediate polars; V709 Cas, NY Lup, and V1223 Sgr in order to determine their masses. From fits to 3–78 keV spectra, we find masses of MWD=0.88+0.05−0.04M⊙, MWD=0.88−0.04+0.05M⊙, 1.16+0.04−0.02M⊙,1.16−0.02+0.04M⊙, and 0.75 ± 0.02 M⊙ for V709 Cas, NY Lup, and V1223 Sgr, respectively. Our measurements are generally in agreement with those determined by previous surveys of intermediate polars, but with typically a factor ∼2 smaller uncertainties. This work paves the way for an approved NuSTAR Legacy Survey of white dwarf masses in intermediate polars.