The evolution of the self-lensing binary KOI-3278: evidence of extra energy sources during CE evolution

¹ Instituto de Física y Astronomía, Universidad de Valparaíso, Av. Gran Bretaña 1111, 5030, Valparaíso Chile
e-mail: mzorotov@dfa.uv.cl
² Millennium Nucleus “Protoplanetary Disks in ALMA Early Science”, Universidad de Valparaíso, Casilla 36- D Santiago, Chile

Received: 18 June 2014
Accepted: 21 July 2014

Abstract

Post-common-envelope binaries (PCEBs) have been frequently used to observationally constrain models of close-compact-binary evolution, in particular common-envelope (CE) evolution. However, recent surveys have detected PCEBs consisting of a white dwarf (WD) exclusively with an M dwarf companion. Thus, we have been essentially blind with respect to PCEBs with more massive companions. Recently, the second PCEB consisting of a WD and a G-type companion, the spectacularly self-lensing binary KOI-3278, has been identified. This system is different from typical PCEBs not only because of the G-type companion, but also because of its long orbital period. Here we investigate whether the existence of KOI-3278 provides new observational constraints on theories of CE evolution. We reconstruct its evolutionary history and predict its future using BSE, clarifying the proper use of the binding energy parameter in this code. We find that a small amount of recombination energy, or any other source of extra energy, is required to reconstruct the evolutionary history of KOI-3278. Using BSE we derive progenitor system parameters of M_1,i = 2.450 M_⊙, M_2,i = 1.034 M_⊙, and P_orb,i ~ 1300 d. We also find that in ~9 Gyr the system will go through a second CE phase leaving behind a double WD, consisting of a C/O WD and a He WD with masses of 0.636 M_⊙ and 0.332 M_⊙, respectively. After IK Peg, KOI-3278 is the second PCEB that clearly requires an extra source of energy, beyond that of orbital energy, to contribute to the CE ejection. Both systems are special in that they have long orbital periods and massive secondaries. This may also indicate that the CE efficiency increases with secondary mass.