Variability of the Spin Period of the White Dwarf in the Magnetic Cataclysmic Binary System EX Hya

TL;DR

This study analyzes the variability of the white dwarf's spin period in the magnetic cataclysmic system EX Hya using observational data and databases, revealing a spin-up timescale and challenging previous mass estimates.

Contribution

It provides new measurements of the white dwarf's spin period variability and refines the ephemeris, offering insights into the system's mass estimates and classification.

Findings

Determined the white dwarf's spin-up timescale as approximately 4.67 million years.

Refined the ephemeris for the maxima of radiation flux related to white dwarf rotation.

Challenged previous mass estimates based on X-ray observations, supporting alternative mass values.

Abstract

The observations of the two-periodic magnetic cataclysmic system EX Hya have been carried out, using the telescopes RC16 and TOA-150 of the Tzec Maun observatory. 6 nights of observations were obtained in 2010-2011 (alternatively changing filters VR). Also the databases of WASP, ASAS and AAVSO have been analyzed. Processing time series was carried out using the program MCV. We analyzed changes in the rotation period of the white dwarf, and based on our own and previously published moments of maximum. The ephemeris was determined for the maxima of the radiation flux associated with the rotation of the magnetic white dwarf: Tmax=2437699.89079(59) +0.0465464808(69).E-6.3(2)*10^{-13}E^2, which corresponds to the characteristic timescale of the rotation spin-up of 4.67(14)*10^6 years. This contradicts the estimated value of the mass of the white dwarf of 0.42M_\odot, based on X-ray observations made by Yuasa et al (2010), however, is consistent with estimates of the masses of 0.79 M_\odot (white dwarf) and 0.108 M_\odot (red dwarf) previously published Beuermann and Reinsch (2008), and the assumption that the capture of accreted plasma by magnetic field of the white dwarf is near the border of the Roche lobe. Analyzed moments do not support the assumption of Mauche et al (2009) for a statistically significant cubic term in the ephemeris. Despite the presence of outbursts in EX Hya, there are significant differences from the DO Dra, which supports the introduction to a detailed classification of the intermediate polars the groups of "outbursting intermediate polars" and "magnetic dwarf novae."