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Cataclysmic variables (CVs) are binaries in which a compact white dwarfaccretes material from a low-mass companion star. The discovery of two planetsin orbit around the CV HU Aquarii opens unusual opportunities for understandingthe formation and evolution of this system. In particular the orbitalparameters of the planets constrains the past and enables us to reconstruct theevolution of the system through the common-envelope phase. During this dramaticevent the entire hydrogen envelope of the primary star is ejected, passing thetwo planets on the way. The observed eccentricities and orbital separations ofthe planets in HU Aqr enable us to limit the common-envelope parameter $\alpha\lambda = 0.45\pm 0.17$ or $\gamma = 1.77\pm0.02$ and measure the rate at whichthe common envelope is ejected, which turns out to be copious. The mass in thecommon envelope is ejected from the binary system at a rate of ${\dot m} =1.9\pm 0.3\,\MSun/yr$. The reconstruction of the initial conditions for HU Aqrindicates that the primary star had a mass of $M_{\rm ZAMS} =1.6\pm0.2$\,\MSun\, and a $m_{\rm ZAMS} = 0.47\pm 0.04$\,\MSun\, companion in a$a=25$--160\,\RSun\, (best value $a=97$\,\RSun) binary. The two planets wereborn with an orbital separation of $a_a=541\pm44$\,\RSun\, and$a_b=750\pm72$\,\Rsun\, respectively. After the common envelope, the primarystar turns into a $0.52\pm0.01$\,\MSun\, helium white dwarf, which subsequentlyaccreted $\sim 0.30$\,\MSun\, from its Roche-lobe filling companion star,grinding it down to its current observed mass of $0.18\,\MSun$.

Planet-Mediated Precision-Reconstruction of the Evolution of the Cataclysmic Variable HU Aquarius