Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-10-23
Mon.Not.Roy.Astron.Soc. 346 (2003) L36
Astronomy and Astrophysics
Astrophysics
5 pages, accepted for publication in MNRAS
Scientific paper
10.1111/j.1365-2966.2003.07317.x
Self-gravitating protostellar discs are unstable to fragmentation if the gas can cool on a time scale that is short compared to the orbital period. We use a combination of hydrodynamic simulations and N-body orbit integrations to study the long term evolution of a fragmenting disc with an initial mass ratio to the star of M_disc/M_star = 0.1. For a disc which is initially unstable across a range of radii, a combination of collapse and subsequent accretion yields substellar objects with a spectrum of masses extending (for a Solar mass star) up to ~0.01 M_sun. Subsequent gravitational evolution ejects most of the lower mass objects within a few million years, leaving a small number of very massive planets or brown dwarfs in eccentric orbits at moderately small radii. Based on these results, systems such as HD 168443 -- in which the companions are close to or beyond the deuterium burning limit -- appear to be the best candidates to have formed via gravitational instability. If massive substellar companions originate from disc fragmentation, while lower-mass planetary companions originate from core accretion, the metallicity distribution of stars which host massive substellar companions at radii of ~1 au should differ from that of stars with lower mass planetary companions.
Armitage Philip J.
Bate Matthew R.
Bonnell Ian A.
Jeffers Sandra V.
Rice W. K. M.
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