University of Cambridge > > DAMTP Astro Lunch > Planetesimal dynamics and growth in tight binary star systems

Planetesimal dynamics and growth in tight binary star systems

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If you have a question about this talk, please contact Jean Teyssandier.

The existence of planets in 20-AU separation binary systems presents an interesting puzzle. It is thought that cores of giant planets form via agglomeration of planetesimals in mutual collisions. However, in tight binary systems, one would naïvely expect the collision velocities between planetesimals to be so high that collisions would destroy even 100 km bodies. Planetesimals are perturbed by gravity from the companion star, and gravity and gas drag from an eccentric gas disk. Because the gas drag acts more strongly on smaller planetesimals, orbital eccentricity depends on planetesimal size. Consequently, planetesimal collision velocities depend on the sizes of the collision partners. The inclusion of disk gravity gives rise to a damaging secular resonance typically at a few AU, however it can also create locations of low relative eccentricity between planetesimals of different sizes.

We run a multi-annulus coagulation/fragmentation simulation to determine the minimum size of initial planetesimal necessary for growth to large sizes in collisions. The minimum initial planetesimal size necessary for growth depends greatly on the disk mass, eccentricity and the degree of apsidal alignment with the binary. We find that in a wide variety of situations, it is a reasonable approximation that growth occurs as long as there are no collisions capable of completely destroying a planetesimal, but erosion by moderately damaging collisions can also prevent growth from occurring.

This talk is part of the DAMTP Astro Lunch series.

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