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

TL;DR

This study uses NuSTAR X-ray spectra to directly measure the masses of white dwarfs in three intermediate polars, achieving more precise results than previous surveys and enabling future large-scale mass measurements.

Contribution

The paper introduces a method to determine white dwarf masses in intermediate polars using NuSTAR spectra, with improved accuracy over prior techniques.

Findings

Masses of V709 Cas, NY Lup, and V1223 Sgr determined with high precision.

Results generally agree with previous surveys but with smaller uncertainties.

Supports future large-scale NuSTAR surveys of white dwarf masses.

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 $M_{\rm WD}=0.88^{+0.05}_{-0.04}M_{\odot}$, $1.16^{+0.04}_{-0.02}M_{\odot}$ and $0.75\pm0.02M_{\odot}$ 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 $\sim2$ smaller uncertainties. This work paves the way for an approved NuSTAR Legacy Survey of white dwarf masses in intermediate polars.