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تسجيل مستخدم جديدInduced planet formation in stellar clusters - a parameter study of star-disk encounters
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Ingo Thies
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We present a parameter study of the possibility of tidally triggered disk instability. Using a restricted N-body model which allows for a survey of an extended parameter space, we show that a passing dwarf star with a mass between 0.1 and 1 M_sun can probably induce gravitational instabilities in the pre-planetary solar disk for prograde passages with minimum separations below 80-170 AU for isothermal or adiabatic disks. Inclined and retrograde encounters lead to similar results but require slightly closer passages. Such encounter distances are quite likely in young moderately massive star clusters (Scally & Clarke 2001; Bonnell et al. 2001). The induced gravitational instabilities may lead to enhanced planetesimal formation in the outer regions of the protoplanetary disk, and could therefore be relevant for the existence of Uranus and Neptune, whose formation timescale of about 100 Myr (Wuchterl, Guillot & Lissauer 2000) is inconsistent with the disk lifetimes of about a few Myr according to observational data by Haisch, Lada & Lada (2001). The relatively small gas/solid ratio in Uranus and Neptune can be matched if the perturbing fly-by occurred after early gas depletion of the solar system, i.e. when the solar system was older than about 5 Myr. We also confirm earlier results by Heller (1993) that the observed 7 degree tilt of the solar equatorial plane relative to the ecliptic plane could be the consequence of such a close encounter.
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Interactions between disc-surrounded stars might play a vital role in the formation of planetary systems. Here a first parameter study of the effects of encounters on low-mass discs is presented. The dependence of the mass and angular momentum transp
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The discovery of planetary systems outside of the solar system has challenged some of the tenets of planetary formation. Among the difficult-to-explain observations, are systems with a giant planet orbiting a very-low mass star, such as the recently
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