PLANET FORMATION IN SMALL SEPARATION BINARIES: NOT SO SECULARLY EXCITED BY THE COMPANION
- Department of Astrophysical Sciences, Princeton University, Ivy Lane, Princeton, NJ 08540 (United States)
The existence of planets in binaries with relatively small separations (around 20 AU), such as {alpha} Centauri or {gamma} Cephei, poses severe challenges to standard planet formation theories. The problem lies in the vigorous secular excitation of planetesimal eccentricities at separations of several AU, where some of the planets are found, by the massive, eccentric stellar companions. High relative velocities of planetesimals preclude their growth in mutual collisions for a wide range of sizes, from below 1 km up to several hundred km, resulting in a fragmentation barrier to planet formation. Here we show that, for the case of an axisymmetric circumstellar protoplanetary disk, the rapid apsidal precession of planetesimal orbits caused by the disk gravity acts to strongly reduce the direct secular eccentricity excitation by the companion, lowering planetesimal velocities by an order of magnitude or even more at 1 AU. By examining the details of planetesimal dynamics, we demonstrate that this effect eliminates the fragmentation barrier for in situ growth of planetesimals as small as {approx}< 10 km even at separations as wide as 2.6 AU (the semimajor axis of the giant planet in HD 196885), provided that the circumstellar protoplanetary disk has a small eccentricity and is relatively massive, {approx}0.1 M{sub Sun }.
- OSTI ID:
- 22130866
- Journal Information:
- Astrophysical Journal Letters, Vol. 765, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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