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THE SIGNATURE OF THE ICE LINE AND MODEST TYPE I MIGRATION IN THE OBSERVED EXOPLANET MASS-SEMIMAJOR AXIS DISTRIBUTION

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Kevin C. Schlaufman1,3, D. N. C. Lin1,4 and S. Ida2

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Existing exoplanet radial velocity surveys are complete in the planetary mass-semimajor axis (Mp -a) plane over the range 0.1 AU <a< 2.0 AU where Mp gsim 100 M . We marginalize over mass in this complete domain of parameter space, and demonstrate that the observed a distribution is inconsistent with models of planet formation that use the full Type I migration rate derived from a linear theory and that do not include the effect of the ice line on the disk surface density profile. However, the efficiency of Type I migration can be suppressed by both nonlinear feedback and the barriers introduced by local maxima in the disk pressure distribution, and we confirm that the synthesized Mp -a distribution is compatible with the observed data if we account for both retention of protoplanetary embryos near the ice line and an order-of-magnitude reduction in the efficiency of Type I migration. The validity of these assumptions can be checked because they also predict a population of short-period rocky planets with a range of masses comparable to that of the Earth as well as a "desert" in the Mp -a distribution centered around Mp ~ 30 – 50 M and a < 1 AU. We show that the expected "desert" in the Mp -a plane will be discernible by a radial velocity survey with 1 m s–1 precision and n ~ 700 radial velocity observations of program stars.


Keywords

planetary systems; planetary systems: formation; planetary systems: protoplanetary disks


Dates

Issue 2 (2009 February 1)

Received 2008 July 23, accepted for publication 2008 September 4

Published 2009 February 3



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