A new scenario for the origin of the 3/2 resonant system HD45364

In this paper we revise the model proposed by Rein et al. (2010) for the origin of the HD45364 exoplanetary system, currently known to host two planets close to the 3/2 mean-motion commensurability (MMR). We show that, due to high surface density of the protoplanetary disk needed for Type III migration, this model could only lead to planets in a quasi-resonant regime of motion, and thus not consistent with the resonant configuration obtained by Correia et al. (2009). Although both resonant and quasi-resonant solutions are statistically indistinguishable with respect to radial velocity measurements, their distinct dynamical behaviour is intriguing. We use the semi-analytical model to confirm the quantitative difference between two configurations. In order to form a system evolving inside the 3/2 resonance, we develop a different model. Our scenario includes an interaction between different (but slower) planetary migration types, planet growth, and gap formation in the protoplanetary disk. The choice of the described evolutionary path was due to a detailed analysis of the structure of the phase space in the vicinity of the 3/2 MMR employing dynamical mapping techniques. The outcomes of our simulations are able to reproduce very closely the 3/2 resonant dynamics obtained from the best-fit presented by Correia et al. (2009). In addition, varying the strength of the eccentricity damping, we can also simulate the quasi-resonant configuration similar to that in Rein et al. (2010). We furthermore show that our scenario is robust with respect to the physical parameters involved in the resonance trapping process. However, the confirmation of our scenario will be possible only with additional radial velocities measurements.