Stability and formation of the resonant system HD 73526

Context. Based on radial velocity measurements, it has been found that the two giant planets detected around the star HD 73526 are in 2: 1 resonance. However, as our numerical integration shows, the derived orbital data for this system result in chaotic behavior of the giant planets, which is uncommon among the resonant extrasolar planetary systems. Aims. We present regular ( non- chaotic) orbital solutions for the giant planets in the system HD 73526 and offer formation scenarios based on combining planetary migration and sudden perturbative effects such as planet- planet scattering or rapid dispersal of the protoplanetary disk. A comparison with the already- studied resonant system HD 128311, exhibiting similar behavior, is given. Methods. The new sets of orbital solutions were derived using the Systemic Console. The stability of these solutions was investigated using the Relative Lyapunov indicator, while the migration and scattering effects are studied by gravitational N- body simulations applying non- conservative forces. Additionally, hydrodynamic simulations of embedded planets in protoplanetary disks were performed to follow the capture into resonance. Results. For the system HD 73526 we demonstrate that the observational radial velocity data are consistent with a coplanar planetary system in a stable 2: 1 resonance exhibiting apsidal corotation. We have shown that, similarly to the system HD 128311, the present dynamical state of HD 73526 could be the result of a mixed evolutionary process combining planetary migration and a perturbative event.