The magnetic cataclysmic variable LSQ1725-64

Abstract

We present new photometry and spectroscopy of the 94m eclipsing binary LSQ1725-64 that provide insight into the fundamental parameters and evolutionary state of this system. We confirm that LSQ1725-64 is a magnetic cataclysmic variable whose white dwarf has a surface-averaged magnetic field strength of $12.5 \pm 0.5$ MG measured from Zeeman splitting. The spectral type and colour of the secondary, as well as the eclipse length, are consistent with other secondaries that have not yet evolved through the period minimum expected for cataclysmic variables. We observe two different states of mass transfer and measure the transition between the two to occur over about 45 orbital cycles. In the low state, we observe photometric variations that we hypothesize to arise predominantly from two previously heated magnetic poles of the white dwarf. Our precise eclipse measurements allow us to determine binary parameters of LSQ1725-64 and we find it contains a high mass ($0.97 \pm 0.03\ M_{\odot}$) white dwarf if we assume a typical mass-radius relationship for a CO core white dwarf. We also measure an eclipse of the accretion stream after the white dwarf eclipse, and use it to estimate an upper limit of the mass transfer rate. This derived limit is consistent with that expected from angular momentum loss via gravitational radiation alone.