6 Perets, H. B. Fig. 3.— The configuration of evolved binary systems vs. their pre-evolved configuration. The pre-evolved binary is a MS- MS binary on a circular orbit with component masses M$_{1}$ = 0 . 8 M$_{⊙}$ and M$_{2}$ = 1 . 6 M$_{⊙}$ , an the evolved binary is a MS- WD binary on a circular orbit with component masses M$_{1}$ = 0 . 8 M$_{⊙}$ and M$_{2}$ = 0 . 6 M$_{⊙}$ . Solid thick line shows the final semi- major axis of binary systems vs. their initial, pre-evolved, semi- major axis. Solid thin line shows the critical semi-major axis a$_{c}$ above which circumbinary planetary orbits are stable in the pre- evolved MS-MS system. Dashed line shows the critical semi-major axis a$_{c}$ above which circumstellar planetary orbits are stable in the evolved MS-WD system. The region between these lines is forbid- den for first generation planetary orbits in the pre-evolved system, but allowed for second generation orbits in the evolved system. (but now looking on inward migration of the binary), circumbinary planetary systems observed to have rela- tively close orbits around their evolved host binary would point to their second generation origin. As described be- low (section 7), such candidate planetary systems have been recently observed. We note, however, that a caveat for such an argument is that pre-exiting first generation planets, if they survive the post-MS evolution, could mi- grate inward (together with the binary, or independently) in the second generation disk. Nevertheless, even the lat- ter case would reflect the existence and importance of a second generation protoplanetary disk and its interaction with first generation planets, as briefly discussed in the next section. Whether such inward migration is a likely consequence presents an interesting question for further studies. Fig. 3, is similar to Fig. 2, but now showing the critical semi-major axis a$_{c}$ for a circumbinary orbit in both the initial (pre-evolved MS-MS binary) and the fi- nal (evolved; MS-WD binary) configuration. Again, the pre and post evolution critical semi-major axis differ sig- nificantly, presenting a region of orbital phase space open only to second generation planets but forbidden for first generation ones. We note in passing, that even non-evolved (low mass) MS close binaries with orbits of a few days were most likely evolved from wider binaries in triple systems, that shrunk to their current orbit due to the processes of Kozai cycles and tidal friction (Mazeh & Shaham 1979; Eggleton & Kisseleva-Eggleton 2006; Tokovinin et al. 2006; Fabrycky & Tremaine 2007). Formation of circumbinary close planetary systems even around short period MS binaries is therefore likely to The replenished gas may also drive a new epoch of planetary migration. Together with the change in plane- tary masses and/or the formation of additional new plan- ets in the system, the previously steady configuration of the planetary systems may now dynamically evolve into a new configuration. Such late dynamical reconfigura- tion could lead to ejection of planets and planetesimals from the system as well as to inward migration and/or possibly infall into their host stars. Ejected planets could become free floating planets. Alternatively these could still be bound to the binary system, in which case fur- ther interactions with either the original host star or the companion would produce a more complicated dynamical history. Several possibilities are opened in this case; the dynamical evolution could lead to a later ejection from the system, infall into one of the stars or a recapture into a more stable circumstellar or circumbinary orbit. All of these possibilities, including the possibility of planet exchange between the binary stars, are not restricted, At the formation epoch of the second generation disk, the accreting star may already host a planetary system. The first generation planetesimals and/or planets could therefore serve as “seeds” for a much more rapid growth of second generation planets. In this case second gen- eration planet formation might behave quite differently than regular planet formation, suggesting a stage where large planetesimals and planets co-exist with and are embedded in a large amount of gaseous material. The first generation planets and planetesimals could now go through an epoch of regrowth (rejuvenation) through ac- cretion of the replenished material. The first generation planets could now grow to become much more massive than typical planets. Moreover, such planetary seeds could induce a more efficient planet formation and pro- duce more massive planets on higher eccentricity orbits (Armitage & Hansen 1999). A possible observational sig- nature of these planets could therefore be their relative larger masses, and possibly higher eccentricity. Whether such regrowth could even lead to a core accretion forma- tion of exceptionally massive planets, effectively becom- ing brown dwarfs (in this case such brown dwarfs could now form much more often in the so called brown dwarf desert regime), is an interesting possibility. Note that in newly formed young binaries late infall of material from the protostellar disk of one star to its companion (the protoplanetary disk of one star may form earlier than that of its companion), may drive similar processes. Such a possibility could explain the existence of more massive close in planets in planet hosting binary systems. If pro- toplanetary disks preferentially form earlier around the more (less) massive component of the binary, more mas- sive close in planets should preferentially form around these components, providing an observational signature for this process. In such regrowth scenarios, more mas- sive planets are likely to form in binaries with closer sep- aration, which could typically form more massive disks. 4. FIRST GENERATION PLANETS IN SECOND GENERATION DISKS be dynamically excluded, or would require a compli- cated and fine tuned dynamical history. Similarly, ex- istence of close planetary systems around blue straggler stars, which were likely formed through similar processes (Perets & Fabrycky 2009) is also unlikely. Initial Semi−major Axis (AU) Final Semi−major Axis (AU) 0 0.5 1 1.5 2 2.5 3 3.5 1 2 3 4 5 6 7 8 First Generation Forbidden Zone