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

Álvarez-Hernández, A.; Torres, M. A. P.; Rodríguez-Gil, P.; Shahbaz, T.; Sánchez-Sierras, J.; Acosta-Pulido, J. A.; Jonker, P. G.; Gazeas, K. D.; Hakala, P.; Corral-Santana, J. M.
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Monthly Notices of the Royal Astronomical Society

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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 K- type donor star K2 = 256 ± 2 km s-1. We also obtain the rotational broadening of its photospheric lines vrot sin i = 141 ± 3 km s-1. From these and the eclipse geometry, we derive a donor-to-white dwarf mass ratio q = M2/M1 = 0.62 ± 0.02, an orbital inclination i = 80.8° ± 0.5° and dynamical masses $M_{1} = 1.21 \pm 0.04 \, \mathrm{M}_{\odot }$ and $M_2 = 0.75 \pm 0.04 \, \mathrm{M}_{\odot }$ (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.
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