We identify SDSSJ121010.1+334722.9 as an eclipsing post-common-envelope binary, with an orbital period of P ~ 3 hrs, containing a very cool, low-mass, DAZ white dwarf and a low-mass main-sequence star of spectral type M5. A model atmosphere analysis of the metal absorption lines detected in the blue part of the optical spectrum, along with the GALEX near-ultraviolet flux, yields a white dwarf temperature of 6000 +/- 200 K and a metallicity value of log(Z/H)= -2.0 +/- 0.3. The sodium absorption doublet is used to measure the radial velocity of the secondary star, K2 ~ 252 km/s and iron absorption lines in the blue part of the spectrum provide the radial velocity of the white dwarf, K1 ~ 95 km/s, yielding a mass ratio of q ~ 0.38. Light curve model fitting, using the Markov Chain Monte Carlo (MCMC) method, gives the inclination angle as i = (79.05 - 79.36) +/- 0.15 degrees, and the stellar masses as M1 = 0.415 +/- 0.010 solar-masses and M2 = 0.158 +/- 0.006 solar-masses. Systematic uncertainties in the absolute calibration of the photometric data influence the determination of the stellar radii. The radius of the white dwarf is found to be R1 = (0.0157 - 0.0161) +/- 0.0003 solar-radii and the volume-averaged radius of the tidally distorted secondary is R2 = (0.197 - 0.203) +/- 0.003 solar-radii. The white dwarf in J1210+3347 is a very strong He-core candidate.

In this work, we study the effects of $\Lambda$-hyperons on neutron star properties employing a metamodel framework for the equation of state (EoS). Different choices for defining the hyperonic couplings with different levels of parametric freedom are discussed. In all models, the predicted NS maximum masses are reduced compared with the purely nucleonic composition as expected. In the case of relating hyperonic couplings via $SU(6)$-symmetry arguments to the nucleonic ones, we find that NS radii for intermediate mass stars are shifted to higher values compared with purely nucleonic stars, in agreement with the existing literature. However, allowing for more freedom for the hyperonic couplings, the effect is strongly reduced, and the distributions in the NS mass-radius plane of models with and without hyperons become very close. We have also investigated how different nucleonic density functionals influence the hyperon matter composition and neutron star properties.