Planetary formation in the gamma Cephei system

Philippe Thébault (1, 2, 3) , Francesco Marzari (4) , Hans Scholl (5) , Diego Turrini (4) , Mauro Barbieri (1, 4, 2, 3)

1 Observatoire de Paris
2 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
3 Pôle Planétologie du LESIA
4 Unipd - Università degli Studi di Padova = University of Padua
5 OCA - Observatoire de la Côte d'Azur

We numerically investigate under which conditions the planet detected at 2.1 AU from gamma Cephei could form through the core-accretion scenario despite the perturbing presence of the highly eccentric companion star. We first show that the initial stage of runaway accretion of kilometer-sized planetesimals is possible within 2.5 AU from the central star only if large amounts of gas are present. In this case, gaseous friction induces periastron alignment of the orbits which reduces the otherwise high mutual impact velocities due to the companion's secular perturbations. The following stage of mutual accretion of large embryos is also modeled. According to our simulations, the giant impacts among the embryos always lead to a core of 10 M_⊕ within 10 Myr, the average lifetime of gaseous discs. However, the core always ends up within 1.5 AU from the central star. Either the core grows more quickly in the inner region of the disc, or it migrates inside by scattering the residual embryos.

Domaines: Astrophysique [astro-ph]

Philippe Thébault, Francesco Marzari, Hans Scholl, Diego Turrini, Mauro Barbieri. Planetary formation in the gamma Cephei system. Astronomy and Astrophysics - A&A, 2004, 427, pp.1097-1104. ⟨10.1051/0004-6361:20040514⟩. ⟨hal-03786607⟩