Properties of the redback millisecond pulsar binary 3FGL J0212.1+5320

Linares et al. obtained quasi-simultaneous g^΄-, r^΄- and i^΄-band light curves and an absorption-line radial velocity curve of the secondary star in the redback system 3FGL J0212.1+5320. The light curves showed two maxima and minima primarily due to the secondary star's ellipsoidal modulation, but with unequal maxima and minima. We fit these light curves and radial velocities with our X-ray binary model including either a dark solar-type star spot or a hotspot due to off-centre heating from an intrabinary shock to account for the unequal maxima. Both models give a radial velocity semi-amplitude and rotational broadening that agree with the observations. The observed secondary star's effective temperature is best matched with the value obtained using the hotspot model, which gives a neutron star and secondary star mass of M₁ = 1.85 ^{+0.32}_{-0.26} M_⊙ and M₂ = 0.50 ^{+0.22}_{-0.19} M_⊙, respectively.