Dynamical mass of the white dwarf in XY Ari: a test for intermediate polar X-ray spectral models

Abstract

<p>We present a dynamical study of the eclipsing intermediate polar XY Ari based on time-resolved near-infrared spectroscopy obtained with the EMIR spectrograph on the 10.4-m Gran Telescopio Canarias. Using main sequence template spectra taken with the same instrument setup as the target spectra, we measure a radial velocity amplitude of the late <em>K</em>- type donor star <em>K</em>₂ = 256 ± 2 km s^-1. We also obtain the rotational broadening of its photospheric lines <em>v</em>_rot sin <em>i</em> = 141 ± 3 km s^-1. From these and the eclipse geometry, we derive a donor-to-white dwarf mass ratio <i>q</i> = <em>M</em>₂/<em>M</em>₁ = 0.62 ± 0.02, an orbital inclination <em>i</em> = 80.8<strong>°</strong> ± 0.5<strong>°</strong> and dynamical masses <em>M</em>₁ = 1.21 ± 0.04 M_⊙ and <em>M</em>₂ = 0.75 ± 0.04 M_⊙ (1σ). This result places the white dwarf in XY Ari as one of the three most massive known in a cataclysmic variable. Comparison with white dwarf mass estimates from X-ray spectral studies could indicate the necessity of an improvement of the X-ray models and/or analysis techniques, as a number of X-ray white dwarf masses are in disagreement with the dynamical mass value.<br></p>